diff --git a/challenges/2023/22-sandSlabs/README.md b/challenges/2023/22-sandSlabs/README.md
new file mode 100644
index 0000000..2cd6d89
--- /dev/null
+++ b/challenges/2023/22-sandSlabs/README.md
@@ -0,0 +1 @@
+# [Day 22: Sand Slabs](https://adventofcode.com/2023/day/22)
diff --git a/challenges/2023/22-sandSlabs/main.py b/challenges/2023/22-sandSlabs/main.py
new file mode 100644
index 0000000..357cc1f
--- /dev/null
+++ b/challenges/2023/22-sandSlabs/main.py
@@ -0,0 +1,146 @@
+import sys
+import gridutil.coord as cu
+from tqdm import tqdm
+
+
+Brick = tuple[cu.Coordinate3, cu.Coordinate3]
+
+
+def parse(instr: str) -> set[Brick]:
+    # (sorry)
+    return set(
+        sorted(
+            [
+                tuple(
+                    sorted(
+                        map(
+                            lambda x: cu.Coordinate3(*map(int, x.split(","))),
+                            line.split("~"),
+                        )
+                    )
+                )
+                for line in instr.splitlines()
+            ],
+            key=lambda x: x[0].z,
+        )
+    )
+
+
+def are_bricks_overlapping(a: Brick, b: Brick) -> bool:
+    x_overlaps = a[0].x <= b[1].x and b[0].x <= a[1].x
+    y_overlaps = a[0].y <= b[1].y and b[0].y <= a[1].y
+    return x_overlaps and y_overlaps
+
+
+def lower_bricks(
+    bricks: set[Brick], start_at: int = 2, return_early: bool = False
+) -> int:
+    max_z = max([x[1].z for x in bricks]) + 1
+    n = 0
+    for level in range(start_at, max_z if not return_early else start_at + 1):
+        present_below = []
+        on_this_level = []
+
+        for brick in bricks:
+            if brick[1].z == level - 1:
+                present_below.append(brick)
+            elif brick[0].z == level:
+                on_this_level.append(brick)
+
+        for brick in on_this_level:
+            overlaps = False
+            for lower_brick in present_below:
+                if are_bricks_overlapping(brick, lower_brick):
+                    overlaps = True
+                    break
+
+            if not overlaps:
+                n += 1
+                # This is what lowering a brick looks like
+                bricks.remove(brick)
+                bricks.add(
+                    (
+                        cu.Coordinate3(brick[0].x, brick[0].y, brick[0].z - 1),
+                        cu.Coordinate3(brick[1].x, brick[1].y, brick[1].z - 1),
+                    )
+                )
+
+    return n
+
+
+def collapse_tower(bricks: set[Brick]):
+    changed = 1
+    while changed != 0:
+        changed = lower_bricks(bricks)
+
+
+def generate_openscad(bricks: set[Brick]) -> str:
+    """
+    This was for debugging
+    """
+    lines = []
+    for brick in bricks:
+        lines.append(
+            "translate(["
+            + (", ".join(map(str, brick[0])))
+            + "]) { cube(["
+            + (
+                ", ".join(
+                    map(str, map(lambda x: 1 + brick[1][x] - brick[0][x], range(3)))
+                )
+            )
+            + "], center=false); };"
+        )
+    return "\n".join(lines)
+
+
+def one(instr: str):
+    bricks = parse(instr)
+
+    _debug("Building initial state", end="\r")
+
+    collapse_tower(bricks)
+
+    acc = 0
+    for brick in tqdm(bricks, desc="Testing individual bricks", file=sys.stderr, leave=False):
+        bc = bricks.copy()
+        bc.remove(brick)
+        v = lower_bricks(bc, start_at=brick[1].z + 1, return_early=True)
+        if v == 0:
+            acc += 1
+
+    return acc
+
+
+def two(instr: str):
+    bricks = parse(instr)
+
+    _debug("Building initial state", end="\r")
+
+    collapse_tower(bricks)
+
+    acc = 0
+    for brick in tqdm(bricks, desc="Testing individual bricks", file=sys.stderr, leave=False):
+        bc = bricks.copy()
+        bc.remove(brick)
+        v = lower_bricks(bc, start_at=brick[1].z + 1)
+        if v != 0:
+            acc += v
+
+    return acc
+
+
+def _debug(*args, **kwargs):
+    kwargs["file"] = sys.stderr
+    print(*args, **kwargs)
+
+
+if __name__ == "__main__":
+    if len(sys.argv) < 2 or sys.argv[1] not in ["1", "2"]:
+        print("Missing day argument", file=sys.stderr)
+        sys.exit(1)
+    inp = sys.stdin.read().strip()
+    if sys.argv[1] == "1":
+        print(one(inp))
+    else:
+        print(two(inp))
diff --git a/challenges/2023/22-sandSlabs/tests.json b/challenges/2023/22-sandSlabs/tests.json
new file mode 100644
index 0000000..39ba35e
--- /dev/null
+++ b/challenges/2023/22-sandSlabs/tests.json
@@ -0,0 +1,14 @@
+{
+    "1": [
+        {
+            "is": "5",
+            "input": "1,0,1~1,2,1\n0,0,2~2,0,2\n0,2,3~2,2,3\n0,0,4~0,2,4\n2,0,5~2,2,5\n0,1,6~2,1,6\n1,1,8~1,1,9\n\n"
+        }
+    ],
+    "2": [
+        {
+            "is": "7",
+            "input": "1,0,1~1,2,1\n0,0,2~2,0,2\n0,2,3~2,2,3\n0,0,4~0,2,4\n2,0,5~2,2,5\n0,1,6~2,1,6\n1,1,8~1,1,9\n\n"
+        }
+    ]
+}
\ No newline at end of file
diff --git a/challenges/2023/README.md b/challenges/2023/README.md
index 34569c0..fcb76e6 100644
--- a/challenges/2023/README.md
+++ b/challenges/2023/README.md
@@ -35,3 +35,4 @@ A day denoted with a star means it has a visualisation.
 | 19 - Aplenty | ★ ★ | Python | So maybe I *can* do range maths? |
 | 20 - Pulse Propagation | ☆ ☆ | Python | Too much reading. |
 | 21 - Step Counter | ★ ☆ | Python | ??? |
+| 21 - Sand Slabs | ★ ★ | Python | I maintain that OpenSCAD is the best AoC 3D debugging tool |
diff --git a/challenges/2023/benchmark-graph.png b/challenges/2023/benchmark-graph.png
index 0a71b7d..d0e6849 100644
Binary files a/challenges/2023/benchmark-graph.png and b/challenges/2023/benchmark-graph.png differ
diff --git a/challenges/2023/benchmarks.jsonl b/challenges/2023/benchmarks.jsonl
index 29de885..a85fb08 100644
--- a/challenges/2023/benchmarks.jsonl
+++ b/challenges/2023/benchmarks.jsonl
@@ -37,3 +37,5 @@
 {"day": 19, "part": 2, "runner": "py", "min": 0.026041030883789062, "max": 0.03458356857299805, "avg": 0.028042428493499756, "n": 100}
 {"day": 19, "part": 1, "runner": "py", "min": 0.023969173431396484, "max": 0.03136777877807617, "avg": 0.026349050998687742, "n": 100}
 {"day": 19, "part": 2, "runner": "py", "min": 0.024805068969726562, "max": 0.03318047523498535, "avg": 0.027637341022491456, "n": 100}
+{"day": 22, "part": 1, "runner": "py", "min": 7.400631666183472, "max": 7.400631666183472, "avg": 7.400631666183472, "n": 1}
+{"day": 22, "part": 2, "runner": "py", "min": 30.386138439178467, "max": 30.386138439178467, "avg": 30.386138439178467, "n": 1}
diff --git a/gridutil/coord.py b/gridutil/coord.py
index c030b85..f8b4563 100644
--- a/gridutil/coord.py
+++ b/gridutil/coord.py
@@ -4,6 +4,7 @@ from numbers import Number
 
 
 Coordinate = namedtuple("Coordinate", ["x", "y"])
+Coordinate3 = namedtuple("Coordinate3", ["x", "y", "z"])
 
 
 def add(a: Coordinate, b: Coordinate) -> Coordinate: