diff --git a/projects/aoc/src/year2021/Solutions2021.kiss b/projects/aoc/src/year2021/Solutions2021.kiss
index 3021e5f9..7724d784 100644
--- a/projects/aoc/src/year2021/Solutions2021.kiss
+++ b/projects/aoc/src/year2021/Solutions2021.kiss
@@ -54,10 +54,17 @@
     (dayTodo 8)
     (day 9
         (load "day9.kiss")
-        (assert (= 4 (count (lowPoints "src/year2021/inputs/day9-example.txt"))))
+        
         // (highlightLowPoints "src/year2021/inputs/day9.txt")
-        (print (apply + (for =>_ height (lowPoints "src/year2021/inputs/day9.txt") (+ 1 height))))
-        )
+        (let [exampleLowPoints (lowPoints "src/year2021/inputs/day9-example.txt")]
+            (assert (= 4 (count exampleLowPoints)))
+            (assert (= 9 (count (basinAround (.next (exampleLowPoints.keys)) "src/year2021/inputs/day9-example.txt")))))
+        (let [realLowPoints (lowPoints "src/year2021/inputs/day9.txt")
+                realBasins (for =>lp _ realLowPoints (basinAround lp "src/year2021/inputs/day9.txt"))
+                basinSizes (for b realBasins (count b))]
+            (assert (= 480 (apply + (for =>_ height realLowPoints (+ 1 height)))))
+            
+            (assert (= 1045660 (apply * (.slice (reversed (sort basinSizes)) 0 3))))))
     (dayTodo 10)
     (dayTodo 11)
     (dayTodo 12)
diff --git a/projects/aoc/src/year2021/day9.kiss b/projects/aoc/src/year2021/day9.kiss
index 41a9216f..1971052c 100644
--- a/projects/aoc/src/year2021/day9.kiss
+++ b/projects/aoc/src/year2021/day9.kiss
@@ -47,6 +47,19 @@
                 (when isLow (dictSet lowPoints key height))))
         lowPoints))
 
+(function :Map<String,Int> basinAround [:String lowPoint file &opt :Map<String,Int> basinAlready :Map<String,Int> allPoints :Map<String,Int> pointsToCheck]
+    (set allPoints (or allPoints (pointMap file)))
+    (set pointsToCheck (or pointsToCheck (pointMap file)))
+    (set basinAlready (or basinAlready (new Map)))
+    (dictSet basinAlready lowPoint (dictGet allPoints lowPoint))
+    (pointsToCheck.remove lowPoint)
+    
+    (doFor =>point _ (adjacentPointMap lowPoint allPoints)
+        (whenLet [(when (< h 9) h) (dictGet pointsToCheck point)]
+            (basinAround point file basinAlready allPoints pointsToCheck)))
+
+    basinAlready)
+
 (function :Void highlightLowPoints [file]
     (let [writer (Ansi.writer (Sys.stdout))
             m (lowPoints file)