diff --git a/2021/inputs/day_12 b/2021/inputs/day_12
new file mode 100644
index 0000000..28bcda4
--- /dev/null
+++ b/2021/inputs/day_12
@@ -0,0 +1,20 @@
+VJ-nx
+start-sv
+nx-UL
+FN-nx
+FN-zl
+end-VJ
+sv-hi
+em-VJ
+start-hi
+sv-em
+end-zl
+zl-em
+hi-VJ
+FN-em
+start-VJ
+jx-FN
+zl-sv
+FN-sv
+FN-hi
+nx-end
diff --git a/2021/solutions/day_12.py b/2021/solutions/day_12.py
new file mode 100644
index 0000000..5deca75
--- /dev/null
+++ b/2021/solutions/day_12.py
@@ -0,0 +1,139 @@
+"""AOC Day 12"""
+
+import pathlib
+import time
+from collections import defaultdict, deque
+
+TEST_INPUT_1 = """start-A
+start-b
+A-c
+A-b
+b-d
+A-end
+b-end"""
+
+TEST_INPUT_2 = """dc-end
+HN-start
+start-kj
+dc-start
+dc-HN
+LN-dc
+HN-end
+kj-sa
+kj-HN
+kj-dc"""
+
+TEST_INPUT_3 = """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"""
+
+def read_input(input_path: str) -> str:
+    """take input file path and return a str with the file's content"""
+    with open(input_path, 'r') as input_file:
+        input_data = input_file.read().strip()
+        return input_data
+
+def extract(input_data: str) -> defaultdict:
+    """take input data and return the appropriate data structure"""
+    graph = defaultdict(list)
+    entries = input_data.split('\n')
+    for entry in entries:
+        a, b = entry.split('-')
+        if b != 'start':
+            graph[a].append(b)
+        if a != 'start':
+            graph[b].append(a) 
+    return graph
+
+def count_paths_1(graph: defaultdict, src: str, dst: str) -> int:
+    stack = deque([(src, {src})])
+    total = 0
+
+    while stack:
+        node, visited = stack.pop()
+        if node == dst:
+            total += 1
+            continue
+
+        for n in graph[node]:
+            if n in visited and n.islower():
+                continue
+            stack.append((n, visited | {n}))
+
+    return total
+
+def count_paths_2(graph: defaultdict, src: str, dst: str) -> int:
+    stack = deque([(src, {src}, False)])
+    total = 0
+
+    while stack:
+        node, visited, double = stack.pop()
+        if node == dst:
+            total += 1
+            continue
+
+        for n in graph[node]:
+            if n not in visited or n.isupper():
+                stack.append((n, visited | {n}, double))
+                continue
+            if double:
+                continue
+            stack.append((n, visited, True))
+
+    return total
+
+def part1(graph: defaultdict) -> int:
+    """part1 solver take the entries and return the part1 solution"""
+    return count_paths_1(graph, 'start', 'end')
+
+def part2(graph: defaultdict) -> int:
+    """part2 solver take the entries and return the part2 solution"""
+    return count_paths_2(graph, 'start', 'end')
+
+def test_input_day_12():
+    """pytest testing function"""
+    entries_1 = extract(TEST_INPUT_1)
+    entries_2 = extract(TEST_INPUT_2)
+    entries_3 = extract(TEST_INPUT_3)
+
+    assert part1(entries_1) == 10
+    assert part1(entries_2) == 19
+    assert part1(entries_3) == 226
+
+    assert part2(entries_1) == 36
+    assert part2(entries_2) == 103
+    assert part2(entries_3) == 3509
+
+
+def test_bench_day_12(benchmark):
+    """pytest-benchmark function"""
+    benchmark(main)
+
+def main():
+    """main function"""
+    input_path = str(pathlib.Path(__file__).resolve().parent.parent) + "/inputs/" + str(pathlib.Path(__file__).stem)
+    start_time = time.time()
+    input_data = read_input(input_path)
+    entries = extract(input_data)
+    print("Part 1: %d" % part1(entries))
+    print("Part 2: %d" % part2(entries))
+    end_time = time.time()
+    print("Execution time: %f" % (end_time-start_time))
+
+if __name__ == "__main__":
+    main()