diff --git a/2020/day17.py b/2020/day17.py
new file mode 100644
index 0000000..9ed3bb6
--- /dev/null
+++ b/2020/day17.py
@@ -0,0 +1,48 @@
+import numpy as np
+with open('input17', 'r') as file:
+  init_state = np.array([[c == '#' for c in l.strip()] for l in file.readlines()])
+
+def sim_step3d(state):
+  new_state = set()
+  neighbours = {}
+  for (x,y,z) in state:
+    for i in (-1,0,1):
+      for j in (-1,0,1):
+        for k in (-1,0,1):
+          neighbours[(x+i,y+j,z+k)] = neighbours.get((x+i,y+j,z+k), 0) + 1
+  for loc, n in neighbours.items():
+    if loc in state:
+      if n in (3,4):  # We added an off-by-one by counting active cubes as their own neighbour for simplicity
+          new_state.add(loc)
+    elif n == 3:
+      new_state.add(loc)
+  return new_state
+
+state = {(x,y,0) for (x, y), v in np.ndenumerate(init_state) if v}
+for i in range(6):
+  state = sim_step3d(state)
+print(f'Part 1: {len(state)}')
+
+
+def sim_step4d(state):
+  new_state = set()
+  neighbours = {}
+  for (x,y,z,u) in state:
+    for i in (-1,0,1):
+      for j in (-1,0,1):
+        for k in (-1,0,1):
+          for l in (-1,0,1):
+            neighbours[(x+i,y+j,z+k,u+l)] = neighbours.get((x+i,y+j,z+k,u+l), 0) + 1
+  for loc, n in neighbours.items():
+    if loc in state:
+      if n in (3,4):  # We added an off-by-one by counting active cubes as their own neighbour for simplicity
+        new_state.add(loc)
+    elif n == 3:
+      new_state.add(loc)
+  return new_state
+
+
+state = {(x,y,0,0) for (x, y), v in np.ndenumerate(init_state) if v}
+for i in range(6):
+    state = sim_step4d(state)
+print(f'Part 2: {len(state)}')
diff --git a/2020/input17 b/2020/input17
new file mode 100644
index 0000000..2869685
--- /dev/null
+++ b/2020/input17
@@ -0,0 +1,8 @@
+##..####
+.###....
+#.###.##
+#....#..
+...#..#.
+#.#...##
+..#.#.#.
+.##...#.