diff --git a/2021/input/2021/day12.txt b/2021/input/2021/day12.txt
new file mode 100644
index 0000000..123aa72
--- /dev/null
+++ b/2021/input/2021/day12.txt
@@ -0,0 +1,22 @@
+zs-WO
+zs-QJ
+WO-zt
+zs-DP
+WO-end
+gv-zt
+iu-SK
+HW-zs
+iu-WO
+gv-WO
+gv-start
+gv-DP
+start-WO
+HW-zt
+iu-HW
+gv-HW
+zs-SK
+HW-end
+zs-end
+DP-by
+DP-iu
+zt-start
diff --git a/2021/src/day12.rs b/2021/src/day12.rs
new file mode 100644
index 0000000..d6b8491
--- /dev/null
+++ b/2021/src/day12.rs
@@ -0,0 +1,96 @@
+use std::{
+    collections::HashMap,
+    fmt::{Debug, Error, Formatter},
+    num::ParseIntError,
+    ops::{Index, IndexMut},
+    str::FromStr,
+};
+
+use anyhow::Result;
+use aoc_runner_derive::{aoc, aoc_generator};
+use thiserror::Error;
+
+struct Node {
+    name: String,
+    small: bool,
+    neighbors: Vec<usize>,
+}
+
+struct Graph {
+    nodes: Vec<String>,
+}
+
+fn search(node: &str, nodes: &HashMap<&str, Vec<&str>>, path: String, paths: &mut Vec<String>) {
+    if node == "end" {
+        paths.push(path);
+        return;
+    }
+    for neighbor in &nodes[node] {
+        // If lowercase.
+        if neighbor.as_bytes()[0] & 0x20 != 0 {
+            if path.contains(neighbor) {
+                continue;
+            }
+        }
+        search(neighbor, nodes, format!("{},{}", path, neighbor), paths);
+    }
+}
+
+fn paths(nodes: &HashMap<&str, Vec<&str>>) -> usize {
+    let mut paths = Vec::new();
+    search("start", nodes, "start".to_string(), &mut paths);
+    //dbg!(&paths);
+    paths.len()
+}
+
+#[aoc(day12, part1)]
+fn part1(input: &str) -> Result<usize> {
+    let mut nodes = HashMap::new();
+    input.lines().for_each(|p| {
+        let (n1, n2) = p.split_once('-').expect("missing dash");
+        nodes.entry(n1).or_insert(Vec::new()).push(n2);
+        nodes.entry(n2).or_insert(Vec::new()).push(n1);
+    });
+    Ok(paths(&nodes))
+}
+
+/*
+#[aoc(day12, part2)]
+fn part2(input: &[u64]) -> Result<u64> {
+todo!("part2");
+Ok(0)
+}
+*/
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part1() -> Result<()> {
+        let input = r#"
+start-A
+start-b
+A-c
+A-b
+b-d
+A-end
+b-end
+"#
+        .trim();
+
+        assert_eq!(part1(input)?, 10);
+        Ok(())
+    }
+
+    /*
+    #[test]
+    fn test_part2()->Result<()> {
+    let input = r#"
+    "#
+    .trim();
+    assert_eq!(part2(&parse(input)?)?, u64::MAX);
+    Ok(())
+    }
+    */
+}
diff --git a/2021/src/lib.rs b/2021/src/lib.rs
index a9465b2..b37d517 100644
--- a/2021/src/lib.rs
+++ b/2021/src/lib.rs
@@ -1,6 +1,7 @@
 pub mod day1;
 pub mod day10;
 pub mod day11;
+pub mod day12;
 pub mod day2;
 pub mod day3;
 pub mod day4;