diff --git a/2021/15/README.md b/2021/15/README.md
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+# 15
+
+Description
+
+<details>
+  <summary>Solutions</summary>
+  <ol>
+    <li>811</li>
+    <li>2</li>
+  </ol>
+</details>
diff --git a/2021/15/python/main.py b/2021/15/python/main.py
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+#!/usr/bin/env python
+
+from os.path import dirname, join
+
+# Day 15
+
+# Common
+
+
+def read_input(filename):
+    data = join(dirname(__file__), '..', filename)
+    with open(data) as f:
+        return f.read().strip()
+
+
+test = read_input('test.txt')
+data = read_input('input.txt')
+
+
+class Cavern:
+    def __init__(self, grid: list[list[int]]) -> None:
+        self.grid = grid
+        self.max_y = len(self.grid)
+        self.max_x = len(self.grid[0])
+
+    def __getitem__(self, index):
+        x, y = index
+        value = self.grid[y % self.max_y][x % self.max_x]
+        extra = y // self.max_y + x // self.max_x
+        if extra:
+            value += extra
+            value = ((value-1) % 9)+1
+        return value
+
+    def find_lowest_risk(self, factor=1):
+        # Calculate lowest cost matrix
+        matrix:  list[list[int]] = []
+        dy = self.max_y*factor
+        dx = self.max_x*factor
+
+        for y in range(dy):
+            matrix.append([])
+            for x in range(dx):
+                if x == 0 and y == 0:
+                    matrix[y].append(0)
+                    continue
+
+                value = self[x, y]
+                lowest = 0
+                if y != 0:
+                    lowest = matrix[y-1][x]
+                if x != 0:
+                    v = matrix[y][x-1]
+                    if lowest == 0 or v < lowest:
+                        lowest = v
+                matrix[y].append(value + lowest)
+
+        return matrix[dy-1][dx-1]
+
+    @staticmethod
+    def parse(data: str):
+        grid = [
+            [int(x) for x in y]
+            for y in data.split('\n')
+        ]
+        return Cavern(grid)
+
+
+        # 1
+print('1.')
+
+cavern = Cavern.parse(test)
+print(cavern.find_lowest_risk())
+cavern = Cavern.parse(data)
+print(cavern.find_lowest_risk())
+
+# 2
+print('\n2.')
+cavern = Cavern.parse(test)
+print(cavern.find_lowest_risk(factor=5))
+cavern = Cavern.parse(data)
+print(cavern.find_lowest_risk(factor=5))