diff --git a/2023/src/day21.clj b/2023/src/day21.clj
new file mode 100644
index 0000000..9033ffc
--- /dev/null
+++ b/2023/src/day21.clj
@@ -0,0 +1,34 @@
+(ns day21
+  (:require
+   [core :refer [get-puzzle-input]]))
+
+(def input (get-puzzle-input 21))
+(def char-map (->> input
+                   (map-indexed (fn [row line]
+                                  (map-indexed (fn [col c]
+                                                 [[row col] c])
+                                               line)))
+                   (apply concat)
+                   (into {})))
+(def start (->> char-map
+                (filter #(= \S (second %)))
+                ffirst))
+(def offsets [[0 1] [0 -1] [1 0] [-1 0]])
+
+;; part 1
+(loop [locs #{start}
+       n 0]
+  (if (< n 64)
+    (recur (->> locs
+                (map (fn [[x y]]
+                       (map (fn [[x-off y-off]]
+                              [(+ x x-off)
+                               (+ y y-off)])
+                            offsets)))
+                (apply concat)
+                (filter #(not= (char-map %)
+                            \#))
+                (into #{}))
+           (inc n))
+    (count locs)))
+