diff --git a/lib/aoc2022/door12.ex b/lib/aoc2022/door12.ex
new file mode 100644
index 0000000..b0e3792
--- /dev/null
+++ b/lib/aoc2022/door12.ex
@@ -0,0 +1,65 @@
+defmodule Aoc2022.Door12 do
+  use Aoc2022.DoorBehaviour
+
+  def run_a(stream) do
+    stream
+    |> Stream.map(&String.trim/1)
+    |> Stream.map(&String.to_charlist/1)
+    |> Stream.with_index()
+    |> Enum.reduce({%{}, nil}, fn {row, index}, {heightmap, goal} ->
+      row
+      |> Enum.with_index()
+      |> Enum.reduce({heightmap, goal}, &convert_row(index, &1, &2))
+    end)
+    |> find_shortest_path()
+  end
+
+  @start ?a
+  @goal ?z
+  defp convert_row(y, {?S, x}, {map, goal}),
+    do: {Map.put(map, {x, y}, {@start, 0, nil}), goal}
+
+  defp convert_row(y, {?E, x}, {map, _}),
+    do: {Map.put(map, {x, y}, {@goal, :infinity, nil}), {x, y}}
+
+  defp convert_row(y, {height, x}, {map, goal}),
+    do: {Map.put(map, {x, y}, {height, :infinity, nil}), goal}
+
+  defp find_shortest_path({heightmap, goal}) do
+    find_shortest_path(heightmap, MapSet.new(Map.keys(heightmap)), goal)
+  end
+
+  defp find_shortest_path(heightmap, remaining, goal) do
+    {{x, y} = min, {level, distance, _}} =
+      heightmap
+      |> Map.take(remaining |> MapSet.to_list())
+      |> Enum.min_by(fn {_, {_, value, _}} -> value end)
+
+    if min == goal do
+      heightmap
+      |> Map.get(goal)
+      |> elem(1)
+    else
+      remaining = MapSet.delete(remaining, min)
+
+      heightmap
+      |> Map.take([{x - 1, y}, {x, y - 1}, {x + 1, y}, {x, y + 1}])
+      |> Enum.filter(fn {key, {other, _, _}} ->
+        level + 1 >= other and MapSet.member?(remaining, key)
+      end)
+      |> Enum.reduce(heightmap, fn {key, {height, other_distance, _}}, map ->
+        new_distance = distance + 1
+
+        if new_distance < other_distance do
+          Map.put(map, key, {height, new_distance, min})
+        else
+          map
+        end
+      end)
+      |> find_shortest_path(remaining, goal)
+    end
+  end
+
+  def run_b(_stream) do
+  end
+end
diff --git a/script/12/input.txt b/script/12/input.txt
new file mode 100644
index 0000000..45dff51
--- /dev/null
+++ b/script/12/input.txt
@@ -0,0 +1,41 @@
+abcccaaaaacccacccccccccccccccccccccccccccccccccccccccccccccccccccccccaaaaaacaccccccaaacccccccccccccccccccccccccccccccccccaaaaaaaaccccccccccccccccccccccccccccccccaaaaaa
+abcccaaaaacccaaacaaacccccccccccccccccaaccccccacccaacccccccccccaacccccaaaaaaaaaaaccaaaaaaccccccccccccccccccccccccccccccccccaaaaaccccccccccccccccccccccccccccccccccaaaaaa
+abccccaaaaaccaaaaaaaccccccccccccccaaaacccccccaacaaacccccccccaaaaaacccaaaaaaaaaaaccaaaaaacccccccccccccccccccccccccccccccccccaaaaaccccccccccccccaaacccccccccccccccccaaaaa
+abccccaacccccaaaaaacccccccccccccccaaaaaacccccaaaaaccccccccccaaaaaacaaaaaaaaaaaaaccaaaaaacccccccccccccccccccccccccccccccccccaacaaccccccccccccccaaaaccccccccccccccccccaaa
+abccccccccccaaaaaaaacccccccccccaaccaaaaaccccccaaaaaacccccccccaaaaacaaaaaaaaccccccccaaaaacccccccccccccccccccccccccccccccccccaacccccccccccccccccaaaaccaaacccccccccccccaac
+abaaaaaccccaaaaaaaaaaccccccaaccaacaaaaacccccaaaaaaaaaaacccccaaaaacaaaacaaaaacccccccaacaacccccccccccccccccccccccccccccccccccccccccccccccccccccccaaaaaaaaacccccccccccaaac
+abaaaaaccccaaaaaaaaaacaacccaaaaaacaccaacccccaaaaaaaaaaacccccaaaaaccccccaaaaaccccccccccaacccccccccccccccccccccccccccccccccccccccccccccccccccccccaaaakkkllccccccccccccccc
+abaaaaacccccccaaacaaaaaaccccaaaaaaaccccccaaacccaacccaaaaaaacccccccccccccaaaaacccccccccaaaaaaccccccccccccccccccccccccccaaccccccccccccccccccccccackkkkkklllccccaaaccccccc
+abaaaaacccccccaaacaaaaaaacccaaaaaaaccccccaaaacaaacaaaaaaaacccccccccccccaaaaaacccccccccaaaaaaccaacaacccccccccccccccaaaaaacccccccccccccccccccaaakkkkkkkkllllcccaaacaccccc
+abaaaaaccccccccaacaaaaaaaacaaaaaaccccccccaaaaaaacaaaaaaaaacccccccccccccaaaacccccccccaaaaaaacccaaaaacccccccccccccccaaaaaaccccccccccccccccjjjjjkkkkkkpppplllcccaaaaaacccc
+abaaaccccccccccccccaaaaaaacaaaaaacccccccccaaaaaaccaaaaaaaccccccccccccccccaaaccccccccaaaaaaaccccaaaaacccccccccccccccaaaaaaaccccaaccccccjjjjjjjkkkkppppppplllcccaaaaacccc
+abccccccccccccccccaaaaaacccccccaaccccccaaaaaaaacccccaaaaaaccccccccccccccccccccccccccccaaaaaaccaaaaaacccccccccccccccaaaaaaaaaacaacccccjjjjjjjjjkooppppppplllcccaaacccccc
+abccccccccccccccccaaaaaacccccccccccccccaaaaaaaaacccaaacaaacccccccccccccccccccccccaaaccaaccaaccaaaaccccccccccccccccaaaaaaaccaaaaaccccjjjjooooooooopuuuupppllccccaaaccccc
+abccccccccccccccccccccaaccccccccccccccccaaaaaaaacccaaaccaacccccccccccccccccccccccaaaaaaacccccccaaaccccccccccccccccaaaaaaccccaaaaaaccjjjoooooooooouuuuuupplllccccaaccccc
+abccaaaaccccaaacccccccccccccccccccccccccccaaaaaaaccaaccccccccccccaacccccccccccccccaaaaacccaaccaaaccccccccccccccccccccaaacccaaaaaaaccjjjoootuuuuuuuuuuuuppllllccccaccccc
+abccaaaaaccaaaacccccccccccccccccccccccccccaacccacccccccccccccccacaaaacccccccccccaaaaaaacccaaaaaaacccccccccccccccccccccccccaaaaaacccciijnoottuuuuuuxxyuvpqqlmmcccccccccc
+abcaaaaaaccaaaacccccccaaaaccccccccccacccccaaccccaaaccccccccccccaaaaaacccccccccccaaaaaaaaccaaaaaacccccccccccccccccaacccccccaacaaacccciiinntttxxxxuxxyyvvqqqqmmmmddddcccc
+abcaaaaaacccaaacccccccaaaaccccaaaaaaaaccaaaaccccaacaacccccccccccaaaaccccccccccccaaaaaaaacccaaaaaaaacccccccccccccaaaaccccccccccaacccciiinntttxxxxxxxyyvvqqqqqmmmmdddcccc
+abcaaaaaacccccccccccccaaaacccccaaaaaacccaaaaaaaaaaaaacccccccccccaaaaccccccccccccccaaacacccaaaaaaaaacccccccccccccaaaacccccccccccccccciiinnnttxxxxxxxyyvvvvqqqqmmmdddcccc
+abcccaaccccccccccccccccaaccccccaaaaaacccaaaaaaaaaaaaaaccccccccccaacaccccccccccccccaaaccccaaaaaaaaaacccccccccccccaaaacccccccccccccccciiinnntttxxxxxyyyyyvvvqqqqmmmdddccc
+SbccccccccccccccccccccccccccccaaaaaaaaccaaaccaaaaaaaaacccccccccccccccccccccccccccccccccccaaaaaaacccccccccaacccccccccccccccccccccccccciiinntttxxxxEzyyyyyvvvqqqmmmdddccc
+abcccccccccccccccccccccccccccaaaaaaaaaacccccccaaaaaacccccccccccccaaacccccaacaacccccccccccccccaaaaaaccccccaacaaacccccccccccccccccccccciiinntttxxxyyyyyyyvvvvqqqmmmdddccc
+abcccccccccccccccccccccccccccaaaaaaaaaaccccccaaaaaaaaccccccccccccaaaccccccaaaacccccccccccccccaaaaaaccccccaaaaacccccccccccccccccccccciiinnnttxxyyyyyyyvvvvvqqqqmmmdddccc
+abcccccccccccccccccccccccccccacacaaacccccccccaaaaaaacccccccccccaaaaaaaacccaaaaacccccccccccccccaaaaaaaacaaaaaaccccccccccccccccccccccciiinntttxxwyyyyywwvvrrrqqmmmdddcccc
+abaccccccccccccccccccccccccccccccaaacccccccccaaacaaaaacccccccccaaaaaaaaccaaaaaacccccccccccccccaaaaaaaacaaaaaaacccccccccccccccccccccchhnnnttwwwwwwwyyywvrrrrnnnnmdddcccc
+abaccccccccccccccccccccccccccccccaaccccccccccccccaaaaaacccccccccaaaaaccccaaaacaccccccccccccccccaaaaacccccaaaaaaccccccaaaccccccaaaccchhnmmttswwwwwwywwwrrrrnnnnneeeccccc
+abaccccccccccccccccccccccccccccccccccccccccccccccaaaaaacccccaaccaaaaaacccccaaccccccccccccccccccaaaaaaccccaaccaaccccaaaaaacccccaaacahhhmmmsssssssswwwwwrrrnnnneeeecccccc
+abaaaccccccccccccccccccccccccccccaaaccccccccccccccaaaaaccccaaaccaaaaaacccccccccccccccccccccccccaaaaaaccccaaccccccccaaaaaacccaaaaaaahhhmmmmsssssssswwwwrrnnnneeeeacccccc
+abaaaccccccccccccccccccccccccccccaaaaaaccccccccccaaaaacaaaaaaaccaaaccaccccccccaaaaaccccccccccccaaaacacccccccccccccccaaaaacccaaaaaaahhhhmmmmssssssswwwwrrnnneeeeaacccccc
+abaaacccccccccccccccccccccccccccaaaaaaaccccccccccaaaaacaaaaaaaaaacccaaaaacccccaaaaacccccccccacaaaaaccacccccccccccccaaaaacccccaaaaaachhhmmmmmmmmmsssrrrrrnnneeeaaaaacccc
+abaccccccccccccccaaaaccccccccccaaaaaaaacccccccccccccccccaaaaaaaaacccaaaaaccccaaaaaacccccccccaaaaaaaaaacccccccccccccaaaaaccccccaaaaachhhhmmmmmmmooossrrronneeeaaaaaacccc
+abaccccccccccccccaaaaccccccccccaaaaaaacccccccccccccccccccaaaaaaaccccaaaaaacccaaaaaaccccaaaccaaaaaaaaaacccccccccccaaccccccccccaaaaaacchhhhhggggooooorrroonnfeeaaaaaccccc
+abcccccccccccccccaaaaccccccccccccaaaaaacccccccccccccccccaaaaaaccccccaaaaaacccaaaaaaccccaaaaaacaaaaaacccccccccaaccaacccccccccccaacccccchhhhggggggoooooooooffeaaaaacccccc
+abccccccccccccccccaacccccccccccccaaaaaacccccccaaccacccccaaaaaaacccccaaaaaaccccaaaccccccaaaaaacaaaaaacccccccccaaaaacccccccccccccccccccccccgggggggggooooooffffaaaaaaccccc
+abccccccccccccccccccccccccccaaaccaacccccccccccaaaaacccccaaccaaacccccccaaacccccccccccccaaaaaaacaaaaaacccccccccaaaaaaaaccccccccccccccccccccccaaaggggfooooffffccccaacccccc
+abaaccccccccccccccccccccccccaaacaccccccccccccaaaaacccccccccccaacccccccaaaacccaacccccccaaaaaaaaaaaaaaaccccccccccaaaaacccccccccccccaaaccccccccccccggfffffffffcccccccccccc
+abaaccccccccccccccccccccccaacaaaaacccccccccccaaaaaacccccccccccccccccccaaaacaaaacccccccaaaaaaaaaccccaccccccccccaaaaaccccccccccccccaaaccccccccccccagfffffffccccccccccccca
+abaacccccccaacccccccccccccaaaaaaaaccccccaacccccaaaacccccccccccccccccccaaaaaaaaacccccccccaaacaacaaacccccccccccaaacaaccccaaccaaccaaaaaaaaccccccccaaaccffffcccccccccccccaa
+abaaaaaaaccaaccccccccccccccaaaaacccccccaaaacccaaccccccccccccccccccacaaaaaaaaaaccccccccccaaacaaaaaacccccccccccccccaaccccaaaaaaccaaaaaaaacccccccccaacccccccccccccccaaacaa
+abaaaaaaaaaaccccccccccccccccaaaaaccccccaaaacccccccccccccccccccccccaaaaaaaaaaaaccccccccccccccaaaaaacccccccccccccccccccccaaaaaacccaaaaaacccccccccaaacccccccccccccccaaaaaa
+abaaaacaaaaaaaacccccccccccccaacaaccccccaaaaccccccccccccccccccccccccaaaaaaaaaaacccccccccccccaaaaaaaacccccccccccccccccccaaaaaaaaccaaaaaaccccccccccccccccccccccccccccaaaaa
diff --git a/test/aoc2022/door12_test.exs b/test/aoc2022/door12_test.exs
new file mode 100644
index 0000000..546c68e
--- /dev/null
+++ b/test/aoc2022/door12_test.exs
@@ -0,0 +1,44 @@
+defmodule Aoc2022.Door12Test do
+  use Aoc2022.DoorCase
+
+  alias Aoc2022.Door12
+
+  @input """
+         Sabqponm
+         abcryxxl
+         accszExk
+         acctuvwj
+         abdefghi
+         """
+         |> fake_stream()
+
+  @input2 """
+          aaabcdefghijaa
+          bjaSaaaaajjjkk
+          clltuaaaajklal
+          dkmsvaaaaaamam
+          ejmrwtsrqponmm
+          finqxuvwxyzEaa
+          ghopyzzzzzzzaa
+          """
+          |> fake_stream()
+
+  @input3 """
+          aaaaaaaaaaaaaaaaaaaaaaaaaaaa
+          aaaaaaaaaaaaaaaaaaaaaaaaaaaa
+          aaaaaaaaaaaaaaaaaaaaaaaaaaaa
+          SabcdefghijklmnopqrstuvwxyzE
+          aaaaaaaaaaaaaaaaaaaaaaaaaaaa
+          aaaaaaaaaaaaaaaaaaaaaaaaaaaa
+          aaaaaaaaaaaaaaaaaaaaaaaaaaaa
+          """
+          |> fake_stream()
+
+  test "run_a/0" do
+    assert 31 == Door12.run_a(@input)
+  end
+
+  test "run_b/0" do
+    assert nil == Door12.run_b(@input)
+  end
+end