diff --git a/day-21/benchmark b/day-21/benchmark
new file mode 100644
index 0000000..a7ec0c4
--- /dev/null
+++ b/day-21/benchmark
@@ -0,0 +1,15 @@
+goos: linux
+goarch: amd64
+pkg: github.com/onyx-and-iris/aoc2024/day-21
+cpu: Intel(R) Core(TM) i7-8700K CPU @ 3.70GHz
+BenchmarkSolve-12    	1000000000	         0.0008915 ns/op
+BenchmarkSolve-12    	1000000000	         0.0007801 ns/op
+BenchmarkSolve-12    	1000000000	         0.0006902 ns/op
+BenchmarkSolve-12    	1000000000	         0.0009074 ns/op
+BenchmarkSolve-12    	1000000000	         0.001131 ns/op
+BenchmarkSolve-12    	1000000000	         0.0008011 ns/op
+BenchmarkSolve-12    	1000000000	         0.001154 ns/op
+BenchmarkSolve-12    	1000000000	         0.0009199 ns/op
+BenchmarkSolve-12    	1000000000	         0.0008066 ns/op
+BenchmarkSolve-12    	1000000000	         0.0008437 ns/op
+ok  	github.com/onyx-and-iris/aoc2024/day-21	0.099s
diff --git a/day-21/cmd/cli/main.go b/day-21/cmd/cli/main.go
new file mode 100644
index 0000000..c85a91a
--- /dev/null
+++ b/day-21/cmd/cli/main.go
@@ -0,0 +1,41 @@
+/********************************************************************************
+    Advent of Code 2024 - day-21
+********************************************************************************/
+
+package main
+
+import (
+	"embed"
+	"flag"
+	"fmt"
+	"slices"
+
+	log "github.com/sirupsen/logrus"
+
+	problems "github.com/onyx-and-iris/aoc2024/day-21"
+)
+
+//go:embed testdata
+var files embed.FS
+
+func main() {
+	filename := flag.String("f", "input.txt", "input file")
+	loglevel := flag.Int("l", int(log.InfoLevel), "log level")
+	flag.Parse()
+
+	if slices.Contains(log.AllLevels, log.Level(*loglevel)) {
+		log.SetLevel(log.Level(*loglevel))
+	}
+
+	data, err := files.ReadFile(fmt.Sprintf("testdata/%s", *filename))
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	one, two, err := problems.Solve(data)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Printf("solution one: %d\nsolution two: %d\n", one, two)
+}
diff --git a/day-21/go.mod b/day-21/go.mod
new file mode 100644
index 0000000..3387108
--- /dev/null
+++ b/day-21/go.mod
@@ -0,0 +1,7 @@
+module github.com/onyx-and-iris/aoc2024/day-21
+
+go 1.23.3
+
+require github.com/sirupsen/logrus v1.9.3
+
+require golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8 // indirect
diff --git a/day-21/go.sum b/day-21/go.sum
new file mode 100644
index 0000000..21f9bfb
--- /dev/null
+++ b/day-21/go.sum
@@ -0,0 +1,15 @@
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/sirupsen/logrus v1.9.3 h1:dueUQJ1C2q9oE3F7wvmSGAaVtTmUizReu6fjN8uqzbQ=
+github.com/sirupsen/logrus v1.9.3/go.mod h1:naHLuLoDiP4jHNo9R0sCBMtWGeIprob74mVsIT4qYEQ=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8 h1:0A+M6Uqn+Eje4kHMK80dtF3JCXC4ykBgQG4Fe06QRhQ=
+golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/day-21/internal/one/benchmark b/day-21/internal/one/benchmark
new file mode 100644
index 0000000..08533ec
--- /dev/null
+++ b/day-21/internal/one/benchmark
@@ -0,0 +1,6 @@
+goos: linux
+goarch: amd64
+pkg: github.com/onyx-and-iris/aoc2024/day-21/internal/one
+cpu: Intel(R) Core(TM) i7-8700K CPU @ 3.70GHz
+BenchmarkSolve-12    	1000000000	         0.0000606 ns/op
+ok  	github.com/onyx-and-iris/aoc2024/day-21/internal/one	0.008s
diff --git a/day-21/internal/one/solve.go b/day-21/internal/one/solve.go
new file mode 100644
index 0000000..fff991a
--- /dev/null
+++ b/day-21/internal/one/solve.go
@@ -0,0 +1,36 @@
+package one
+
+import (
+	"bytes"
+
+	"github.com/onyx-and-iris/aoc2024/day-21/internal/pad"
+	log "github.com/sirupsen/logrus"
+)
+
+func Solve(buf []byte) (int, error) {
+	r := bytes.NewReader(buf)
+	codes, err := parseLines(r)
+	if err != nil {
+		return 0, err
+	}
+
+	numpad := pad.NewNumpad()
+	dirpad := pad.NewDirpad()
+
+	var complexity int
+	for _, code := range codes {
+		moves := generateMoves(numpad, dirpad, code)
+		complexity += len(moves) * numFromCode(code)
+		log.Debugf("%s\n%d * %d\n", moves, len(moves), numFromCode(code))
+	}
+
+	return complexity, nil
+}
+
+type generator interface {
+	Generate(code string) string
+}
+
+func generateMoves(n, d generator, code string) string {
+	return d.Generate(d.Generate(n.Generate(code)))
+}
diff --git a/day-21/internal/one/solve_internal_test.go b/day-21/internal/one/solve_internal_test.go
new file mode 100644
index 0000000..e5fd7ea
--- /dev/null
+++ b/day-21/internal/one/solve_internal_test.go
@@ -0,0 +1,15 @@
+package one
+
+import (
+	_ "embed"
+	"os"
+	"testing"
+)
+
+//go:embed testdata/input.txt
+var data []byte
+
+func BenchmarkSolve(b *testing.B) {
+	os.Stdout, _ = os.Open(os.DevNull)
+	Solve(data)
+}
diff --git a/day-21/internal/one/util.go b/day-21/internal/one/util.go
new file mode 100644
index 0000000..061c3d1
--- /dev/null
+++ b/day-21/internal/one/util.go
@@ -0,0 +1,27 @@
+package one
+
+import (
+	"bufio"
+	"io"
+	"strconv"
+)
+
+func parseLines(r io.Reader) ([]string, error) {
+	codes := []string{}
+
+	scanner := bufio.NewScanner(r)
+	for scanner.Scan() {
+		codes = append(codes, scanner.Text())
+	}
+
+	if err := scanner.Err(); err != nil {
+		return nil, err
+	}
+
+	return codes, nil
+}
+
+func numFromCode(s string) int {
+	n, _ := strconv.Atoi(s[:len(s)-1])
+	return n
+}
diff --git a/day-21/internal/pad/dirpad.go b/day-21/internal/pad/dirpad.go
new file mode 100644
index 0000000..d2aa1ab
--- /dev/null
+++ b/day-21/internal/pad/dirpad.go
@@ -0,0 +1,106 @@
+package pad
+
+import (
+	"slices"
+	"strings"
+
+	log "github.com/sirupsen/logrus"
+)
+
+type Dirpad struct {
+	current   node
+	pad       [][]rune
+	locations map[rune]coords
+}
+
+func NewDirpad() *Dirpad {
+	pad := [][]rune{
+		{'.', '^', 'A'},
+		{'<', 'v', '>'},
+	}
+	locations := make(map[rune]coords)
+	for y, row := range pad {
+		for x, value := range row {
+			locations[value] = coords{x, y}
+		}
+	}
+
+	return &Dirpad{
+		current:   newNode(2, 0, 'A'),
+		pad:       pad,
+		locations: locations,
+	}
+}
+
+func (dp *Dirpad) valueAt(c coords) rune {
+	return dp.pad[c.y][c.x]
+}
+
+func (dp *Dirpad) nextTarget(c rune) node {
+	coords := dp.locations[c]
+	return newNode(coords.x, coords.y, c)
+}
+
+func (dp *Dirpad) Generate(code string) string {
+	var sb strings.Builder
+	for _, c := range code {
+		target := dp.nextTarget(c)
+		moved := newMove(dp.current.x, target.x, dp.current.y, target.y)
+
+		var hb, vb strings.Builder
+
+		for range absInt(moved.x) {
+			if moved.x >= 0 {
+				hb.WriteRune('>')
+			} else {
+				hb.WriteRune('<')
+			}
+		}
+
+		for range absInt(moved.y) {
+			if moved.y <= 0 {
+				vb.WriteRune('^')
+			} else {
+				vb.WriteRune('v')
+			}
+		}
+
+		if dp.valueAt(coords{dp.current.x + moved.x, dp.current.y}) == '.' {
+			sb.WriteString(vb.String())
+			sb.WriteString(hb.String())
+		} else if dp.valueAt(coords{dp.current.x, dp.current.y + moved.y}) == '.' {
+			sb.WriteString(hb.String())
+			sb.WriteString(vb.String())
+		} else if moved.x < 0 {
+			sb.WriteString(hb.String())
+			sb.WriteString(vb.String())
+		} else if moved.x >= 0 {
+			sb.WriteString(vb.String())
+			sb.WriteString(hb.String())
+		}
+
+		sb.WriteRune('A')
+		dp.current = target
+	}
+
+	log.Tracef("\n%s\n", dp.trace(sb.String()))
+
+	return sb.String()
+}
+
+func (dp *Dirpad) trace(visited string) string {
+	log.Debug(visited)
+	temp := slices.Clone(dp.pad)
+
+	next := coords{2, 0}
+	for _, c := range visited {
+		next = neighbours(next, c)
+		temp[next.y][next.x] = 'X'
+	}
+
+	output := []string{}
+	for _, row := range temp {
+		output = append(output, string(row))
+	}
+	return strings.Join(output, "\n")
+}
diff --git a/day-21/internal/pad/move.go b/day-21/internal/pad/move.go
new file mode 100644
index 0000000..0ea3e66
--- /dev/null
+++ b/day-21/internal/pad/move.go
@@ -0,0 +1,12 @@
+package pad
+
+type move struct {
+	x, y int
+}
+
+func newMove(x1, x2, y1, y2 int) *move {
+	return &move{
+		x: x2 - x1,
+		y: y2 - y1,
+	}
+}
diff --git a/day-21/internal/pad/neighbours.go b/day-21/internal/pad/neighbours.go
new file mode 100644
index 0000000..ac31895
--- /dev/null
+++ b/day-21/internal/pad/neighbours.go
@@ -0,0 +1,16 @@
+package pad
+
+func neighbours(c coords, r rune) coords {
+	switch r {
+	case '^':
+		return coords{c.x, c.y - 1}
+	case '>':
+		return coords{c.x + 1, c.y}
+	case 'v':
+		return coords{c.x, c.y + 1}
+	case '<':
+		return coords{c.x - 1, c.y}
+	default:
+		return c
+	}
+}
diff --git a/day-21/internal/pad/node.go b/day-21/internal/pad/node.go
new file mode 100644
index 0000000..5545733
--- /dev/null
+++ b/day-21/internal/pad/node.go
@@ -0,0 +1,14 @@
+package pad
+
+type coords struct {
+	x, y int
+}
+
+type node struct {
+	coords
+	value rune
+}
+
+func newNode(x, y int, value rune) node {
+	return node{coords: coords{x, y}, value: value}
+}
diff --git a/day-21/internal/pad/numpad.go b/day-21/internal/pad/numpad.go
new file mode 100644
index 0000000..b9d2efe
--- /dev/null
+++ b/day-21/internal/pad/numpad.go
@@ -0,0 +1,108 @@
+package pad
+
+import (
+	"slices"
+	"strings"
+
+	log "github.com/sirupsen/logrus"
+)
+
+type Numpad struct {
+	current   node
+	pad       [][]rune
+	locations map[rune]coords
+}
+
+func NewNumpad() *Numpad {
+	pad := [][]rune{
+		{'7', '8', '9'},
+		{'4', '5', '6'},
+		{'1', '2', '3'},
+		{'.', '0', 'A'},
+	}
+	locations := make(map[rune]coords)
+	for y, row := range pad {
+		for x, value := range row {
+			locations[value] = coords{x, y}
+		}
+	}
+
+	return &Numpad{
+		current:   newNode(2, 3, 'A'),
+		pad:       pad,
+		locations: locations,
+	}
+}
+
+func (np *Numpad) valueAt(c coords) rune {
+	return np.pad[c.y][c.x]
+}
+
+func (np *Numpad) nextTarget(c rune) node {
+	coords := np.locations[c]
+	return newNode(coords.x, coords.y, c)
+}
+
+func (np *Numpad) Generate(code string) string {
+	var sb strings.Builder
+	for _, c := range code {
+		target := np.nextTarget(c)
+		moved := newMove(np.current.x, target.x, np.current.y, target.y)
+
+		var hb, vb strings.Builder
+
+		for range absInt(moved.x) {
+			if moved.x >= 0 {
+				hb.WriteRune('>')
+			} else {
+				hb.WriteRune('<')
+			}
+		}
+
+		for range absInt(moved.y) {
+			if moved.y <= 0 {
+				vb.WriteRune('^')
+			} else {
+				vb.WriteRune('v')
+			}
+		}
+
+		if np.valueAt(coords{np.current.x + moved.x, np.current.y}) == '.' {
+			sb.WriteString(vb.String())
+			sb.WriteString(hb.String())
+		} else if np.valueAt(coords{np.current.x, np.current.y + moved.y}) == '.' {
+			sb.WriteString(hb.String())
+			sb.WriteString(vb.String())
+		} else if moved.x < 0 {
+			sb.WriteString(hb.String())
+			sb.WriteString(vb.String())
+		} else if moved.x >= 0 {
+			sb.WriteString(vb.String())
+			sb.WriteString(hb.String())
+		}
+
+		sb.WriteRune('A')
+		np.current = target
+	}
+
+	log.Tracef("\n%s\n", np.trace(sb.String()))
+
+	return sb.String()
+}
+
+func (np *Numpad) trace(visited string) string {
+	log.Debug(visited)
+	temp := slices.Clone(np.pad)
+
+	next := coords{2, 3}
+	for _, c := range visited {
+		next = neighbours(next, c)
+		temp[next.y][next.x] = 'X'
+	}
+
+	output := []string{}
+	for _, row := range temp {
+		output = append(output, string(row))
+	}
+	return strings.Join(output, "\n")
+}
diff --git a/day-21/internal/pad/util.go b/day-21/internal/pad/util.go
new file mode 100644
index 0000000..97b86bd
--- /dev/null
+++ b/day-21/internal/pad/util.go
@@ -0,0 +1,7 @@
+package pad
+
+import "math"
+
+func absInt(n int) int {
+	return int(math.Abs(float64(n)))
+}
diff --git a/day-21/internal/two/benchmark b/day-21/internal/two/benchmark
new file mode 100644
index 0000000..af72586
--- /dev/null
+++ b/day-21/internal/two/benchmark
@@ -0,0 +1,6 @@
+goos: linux
+goarch: amd64
+pkg: github.com/onyx-and-iris/aoc2024/day-21/internal/two
+cpu: Intel(R) Core(TM) i7-8700K CPU @ 3.70GHz
+BenchmarkSolve-12    	1000000000	         0.0007436 ns/op
+ok  	github.com/onyx-and-iris/aoc2024/day-21/internal/two	0.011s
diff --git a/day-21/internal/two/cache.go b/day-21/internal/two/cache.go
new file mode 100644
index 0000000..a9bac56
--- /dev/null
+++ b/day-21/internal/two/cache.go
@@ -0,0 +1,41 @@
+package two
+
+import "sync"
+
+type robotCache struct {
+	mu   *sync.RWMutex
+	data map[string]map[int]int
+}
+
+func newRobotCache() robotCache {
+	return robotCache{
+		mu:   &sync.RWMutex{},
+		data: make(map[string]map[int]int),
+	}
+}
+
+func (rc *robotCache) read(moves string, id int) (int, bool) {
+	rc.mu.RLock()
+	defer rc.mu.RUnlock()
+
+	v, ok := rc.data[moves][id]
+	return v, ok
+}
+
+func (rc *robotCache) contains(moves string) bool {
+	rc.mu.RLock()
+	defer rc.mu.RUnlock()
+
+	_, ok := rc.data[moves]
+	return ok
+}
+
+func (rc *robotCache) insert(moves string, id, val int) {
+	rc.mu.Lock()
+	defer rc.mu.Unlock()
+
+	if _, ok := rc.data[moves]; !ok {
+		rc.data[moves] = make(map[int]int)
+	}
+	rc.data[moves][id] = val
+}
diff --git a/day-21/internal/two/solve.go b/day-21/internal/two/solve.go
new file mode 100644
index 0000000..92f77f2
--- /dev/null
+++ b/day-21/internal/two/solve.go
@@ -0,0 +1,71 @@
+package two
+
+import (
+	"bytes"
+	"strings"
+
+	"github.com/onyx-and-iris/aoc2024/day-21/internal/pad"
+)
+
+func Solve(buf []byte) (int, error) {
+	r := bytes.NewReader(buf)
+	codes, err := parseLines(r)
+	if err != nil {
+		return 0, err
+	}
+
+	complexityChan := make(chan int)
+	conc := len(codes)
+
+	for _, code := range codes {
+		go func() {
+			numpad := pad.NewNumpad()
+			dirpad := pad.NewDirpad()
+			complexityChan <- numFromCode(code) * generateIntFromMoves(numpad, dirpad, code, 25)
+		}()
+	}
+
+	var complexity int
+	for range conc {
+		complexity += <-complexityChan
+	}
+
+	return complexity, nil
+}
+
+type generator interface {
+	Generate(code string) string
+}
+
+func generateIntFromMoves(n, d generator, code string, numRobots int) int {
+	moves := n.Generate(code)
+	return recurseForRobots(d, moves, numRobots, 1, newRobotCache())
+}
+
+func recurseForRobots(
+	d generator,
+	moves string,
+	numRobots int,
+	id int,
+	memo robotCache,
+) int {
+	if memo.contains(moves) {
+		if v, ok := memo.read(moves, id-1); ok {
+			return v
+		}
+	}
+
+	next := d.Generate(moves)
+	if id == numRobots {
+		return len(next)
+	}
+
+	var totalCount int
+	for _, move := range strings.SplitAfter(next, "A") {
+		count := recurseForRobots(d, move, numRobots, id+1, memo)
+		totalCount += count
+	}
+	memo.insert(moves, id-1, totalCount)
+
+	return totalCount
+}
diff --git a/day-21/internal/two/solve_internal_test.go b/day-21/internal/two/solve_internal_test.go
new file mode 100644
index 0000000..ecb05d5
--- /dev/null
+++ b/day-21/internal/two/solve_internal_test.go
@@ -0,0 +1,15 @@
+package two
+
+import (
+	_ "embed"
+	"os"
+	"testing"
+)
+
+//go:embed testdata/input.txt
+var data []byte
+
+func BenchmarkSolve(b *testing.B) {
+	os.Stdout, _ = os.Open(os.DevNull)
+	Solve(data)
+}
diff --git a/day-21/internal/two/util.go b/day-21/internal/two/util.go
new file mode 100644
index 0000000..63698f9
--- /dev/null
+++ b/day-21/internal/two/util.go
@@ -0,0 +1,27 @@
+package two
+
+import (
+	"bufio"
+	"io"
+	"strconv"
+)
+
+func parseLines(r io.Reader) ([]string, error) {
+	codes := []string{}
+
+	scanner := bufio.NewScanner(r)
+	for scanner.Scan() {
+		codes = append(codes, scanner.Text())
+	}
+
+	if err := scanner.Err(); err != nil {
+		return nil, err
+	}
+
+	return codes, nil
+}
+
+func numFromCode(s string) int {
+	n, _ := strconv.Atoi(s[:len(s)-1])
+	return n
+}
diff --git a/day-21/makefile b/day-21/makefile
new file mode 100644
index 0000000..98796ed
--- /dev/null
+++ b/day-21/makefile
@@ -0,0 +1,30 @@
+program = day-21
+
+GO = go
+SRC_DIR := src
+BIN_DIR := bin
+
+EXE := $(BIN_DIR)/$(program)
+
+.DEFAULT_GOAL := build
+
+.PHONY: fmt vet build bench clean
+fmt:        
+	$(GO) fmt ./...
+
+vet: fmt        
+	$(GO) vet ./...
+
+build: vet | $(BIN_DIR)
+	$(GO) build -o $(EXE) ./$(SRC_DIR)
+
+bench:
+	$(GO) test ./internal/one/ -bench=. > internal/one/benchmark
+	$(GO) test ./internal/two/ -bench=. > internal/two/benchmark
+	$(GO) test . -count=10 -bench=. > benchmark
+
+$(BIN_DIR):
+	@mkdir -p $@
+
+clean:
+	@rm -rv $(BIN_DIR)
diff --git a/day-21/solve.go b/day-21/solve.go
new file mode 100644
index 0000000..3e4e84f
--- /dev/null
+++ b/day-21/solve.go
@@ -0,0 +1,20 @@
+package daytwentyone
+
+import (
+	"github.com/onyx-and-iris/aoc2024/day-21/internal/one"
+	"github.com/onyx-and-iris/aoc2024/day-21/internal/two"
+)
+
+func Solve(buf []byte) (int, int, error) {
+	answerOne, err := one.Solve(buf)
+	if err != nil {
+		return 0, 0, err
+	}
+
+	answerTwo, err := two.Solve(buf)
+	if err != nil {
+		return 0, 0, err
+	}
+
+	return answerOne, answerTwo, nil
+}
diff --git a/day-21/solve_internal_test.go b/day-21/solve_internal_test.go
new file mode 100644
index 0000000..6c2b2ca
--- /dev/null
+++ b/day-21/solve_internal_test.go
@@ -0,0 +1,15 @@
+package daytwentyone
+
+import (
+	_ "embed"
+	"os"
+	"testing"
+)
+
+//go:embed testdata/input.txt
+var data []byte
+
+func BenchmarkSolve(b *testing.B) {
+	os.Stdout, _ = os.Open(os.DevNull)
+	Solve(data)
+}