diff --git a/source/app.d b/source/app.d
index 153ffa9..7da990b 100644
--- a/source/app.d
+++ b/source/app.d
@@ -1,7 +1,7 @@
 import std.stdio;
 
-import day11.part1;
+import day12.part1;
 
 void main() {
-	dumboOctopus();
+	passagePathing();
 }
diff --git a/source/day12/input.txt b/source/day12/input.txt
new file mode 100644
index 0000000..1d5c9fe
--- /dev/null
+++ b/source/day12/input.txt
@@ -0,0 +1,24 @@
+re-js
+qx-CG
+start-js
+start-bj
+qx-ak
+js-bj
+ak-re
+CG-ak
+js-CG
+bj-re
+ak-lg
+lg-CG
+qx-re
+WP-ak
+WP-end
+re-lg
+end-ak
+WP-re
+bj-CG
+qx-start
+bj-WP
+JG-lg
+end-lg
+lg-iw
diff --git a/source/day12/part1.d b/source/day12/part1.d
new file mode 100644
index 0000000..5ecded9
--- /dev/null
+++ b/source/day12/part1.d
@@ -0,0 +1,73 @@
+module day12.part1;
+
+import std.file;
+import std.stdio;
+import std.string;
+import std.algorithm;
+import std.conv;
+import std.array;
+
+bool isLarge(string name) {
+    return name.toUpper() == name;
+}
+
+void registerPath(ref string[][string] paths, string[] caves) {
+    if (caves[0] !in paths) {
+        paths[caves[0]] = [caves[1]];
+    } else {
+        paths[caves[0]] ~= caves[1];
+    }
+    if (caves[1] !in paths) {
+        paths[caves[1]] = [caves[0]];
+    } else {
+        paths[caves[1]] ~= caves[0];
+    }
+}
+
+uint[string] getVisitCounts(string[] history) {
+    uint[string] visitCounts;
+    foreach (p; history) {
+        if (p !in visitCounts) {
+            visitCounts[p] = 1;
+        } else {
+            visitCounts[p]++;
+        }
+    }
+    return visitCounts;
+}
+
+bool canVisit(string cave, string[] history) {
+    if (cave.isLarge) return true;
+    uint[string] visitCounts = getVisitCounts(history);
+    bool visitedSmallCaveTwice = false;
+    foreach (p, c; visitCounts) {
+        if (!p.isLarge && c > 1) {
+            visitedSmallCaveTwice = true;
+            break;
+        }
+    }
+    uint availablePathVisitCount = visitCounts.require(cave, 0);
+    return visitedSmallCaveTwice ? availablePathVisitCount < 1 : availablePathVisitCount < 2;
+}
+
+string[][] findPaths(ref string[][string] paths, string cave, string[] history) {
+    if (cave == "end") return [history ~ cave];
+    string[][] nextPaths = [];
+    foreach (availablePath; paths[cave]) {
+        if (availablePath == "start") continue;
+        if (canVisit(availablePath, history ~ cave)) nextPaths ~= findPaths(paths, availablePath, history ~ cave);
+    }
+    return nextPaths;
+}
+
+void passagePathing() {
+    string[] pathDescriptors = readText("source/day12/input.txt").strip.split("\n")
+        .map!(s => s.strip).array;
+    string[][string] paths;
+    foreach (desc; pathDescriptors) {
+        registerPath(paths, desc.split("-"));
+    }
+    findPaths(paths, "start", [])
+        .map!(p => p.joiner!(string[], string)(",").to!string)
+        .array.length.writeln;
+}
\ No newline at end of file
diff --git a/source/day12/test_input.txt b/source/day12/test_input.txt
new file mode 100644
index 0000000..6fd8c41
--- /dev/null
+++ b/source/day12/test_input.txt
@@ -0,0 +1,7 @@
+start-A
+start-b
+A-c
+A-b
+b-d
+A-end
+b-end
diff --git a/source/day12/test_input2.txt b/source/day12/test_input2.txt
new file mode 100644
index 0000000..62cc714
--- /dev/null
+++ b/source/day12/test_input2.txt
@@ -0,0 +1,10 @@
+dc-end
+HN-start
+start-kj
+dc-start
+dc-HN
+LN-dc
+HN-end
+kj-sa
+kj-HN
+kj-dc
diff --git a/source/day12/test_input3.txt b/source/day12/test_input3.txt
new file mode 100644
index 0000000..65f3833
--- /dev/null
+++ b/source/day12/test_input3.txt
@@ -0,0 +1,18 @@
+fs-end
+he-DX
+fs-he
+start-DX
+pj-DX
+end-zg
+zg-sl
+zg-pj
+pj-he
+RW-he
+fs-DX
+pj-RW
+zg-RW
+start-pj
+he-WI
+zg-he
+pj-fs
+start-RW