diff --git a/2021/day12.py b/2021/day12.py
new file mode 100644
index 0000000..cf14dfb
--- /dev/null
+++ b/2021/day12.py
@@ -0,0 +1,38 @@
+from collections import defaultdict
+from string import ascii_lowercase
+
+with open("input12.txt") as f:
+    lines = [line.rstrip() for line in f]
+cxs = defaultdict(list)
+for a, b in map(lambda s: s.split("-"), lines):
+    cxs[a].append(b)
+    cxs[b].append(a)
+
+
+def walk(path, skip_f):
+    if path[-1] == "end":
+        return [path]
+    valid_paths = []
+    for cave in filter(lambda c: c != "start", cxs[path[-1]]):
+        if skip_f(cave, path):
+            continue
+        valid_paths += walk(path + [cave], skip_f)
+    return valid_paths
+
+
+def skip1(cave, path):
+    return cave[0] in ascii_lowercase and cave in path
+
+
+def skip2(cave, path):
+    return (
+        skip1(cave, path)
+        and any(
+            path.count(c) > 1
+            for c in filter(lambda c: c[0] in ascii_lowercase, path)
+        )
+    )
+
+
+print(len(walk(["start"], skip1)))
+print(len(walk(["start"], skip2)))