diff --git a/12/input b/12/input
new file mode 100644
index 0000000..96b504b
--- /dev/null
+++ b/12/input
@@ -0,0 +1,23 @@
+vn-DD
+qm-DD
+MV-xy
+end-xy
+KG-end
+end-kw
+qm-xy
+start-vn
+MV-vn
+vn-ko
+lj-KG
+DD-xy
+lj-kh
+lj-MV
+ko-MV
+kw-qm
+qm-MV
+lj-kw
+VH-lj
+ko-qm
+ko-start
+MV-start
+DD-ko
diff --git a/12/part1.php b/12/part1.php
new file mode 100644
index 0000000..bf9f145
--- /dev/null
+++ b/12/part1.php
@@ -0,0 +1,29 @@
+<?php
+$input = file('input', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
+$input = array_map(fn($line) => explode('-', $line), $input);
+
+$adjacencyList = [];
+foreach ($input as $key => $item) {
+    if ($item[1] != 'start') $adjacencyList[$item[0]][] = $item[1];
+    if ($item[0] != 'start') $adjacencyList[$item[1]][] = $item[0];
+}
+$history = [];
+echo track($adjacencyList, "start", $history);
+function track($adjacencyList, $cave, $history) {
+    $count = 0;
+    $history[] = $cave;
+    foreach($adjacencyList[$cave] as $path) {
+        if(strtolower($path) === $path && in_array($path,$history)) {
+            //bad path, go no further
+        }
+        else if($path == "end") {
+            $count += 1;
+            echo implode(",",$history) ."\n";
+        }
+        else {
+            $count += track($adjacencyList, $path, $history);
+        }
+    }
+    return $count;
+}
+
diff --git a/12/part2.php b/12/part2.php
new file mode 100644
index 0000000..cbe6b6f
--- /dev/null
+++ b/12/part2.php
@@ -0,0 +1,31 @@
+<?php
+$input = file('input', FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);
+$input = array_map(fn($line) => explode('-', $line), $input);
+
+$adjacencyList = [];
+foreach ($input as $key => $item) {
+    if ($item[1] != 'start') $adjacencyList[$item[0]][] = $item[1];
+    if ($item[0] != 'start') $adjacencyList[$item[1]][] = $item[0];
+}
+$history = [];
+echo track($adjacencyList, "start", $history, 0);
+
+function track($adjacencyList, $cave, $history, $doubled)
+{
+    $count = 0;
+    $history[] = $cave;
+    foreach ($adjacencyList[$cave] as $path) {
+        //small cave, not already visited
+        if ($path == "start") {
+        } elseif (strtolower($path) === $path && in_array($path, $history)) {
+            if ($doubled == 0) {
+                $count += track($adjacencyList, $path, $history, 1);
+            }
+        } elseif ($path == "end") {
+            $count += 1;
+        } else {
+            $count += track($adjacencyList, $path, $history, $doubled);
+        }
+    }
+    return $count;
+}
diff --git a/README.md b/README.md
index 93cfb09..b673ae2 100644
--- a/README.md
+++ b/README.md
@@ -53,4 +53,10 @@
 ### DAY 11 - Dumbo octopus
 
 - [part1](11/part1.php)
-- [part2](11/part2.php)
\ No newline at end of file
+- [part2](11/part2.php)
+
+
+### DAY 12 - Linked caves
+
+- [part1](12/part1.php)
+- [part2](12/part2.php)
\ No newline at end of file