diff --git a/src/Year_2021/P9.py b/src/Year_2021/P9.py
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+# --- Day 9: Smoke Basin ---
+
+# These caves seem to be lava tubes. Parts are even still volcanically active;
+# small hydrothermal vents release smoke into the caves that slowly settles
+# like rain.
+
+# If you can model how the smoke flows through the caves, you might be able to
+# avoid it and be that much safer. The submarine generates a heightmap of the
+# floor of the nearby caves for you (your puzzle input).
+
+# Smoke flows to the lowest point of the area it's in. For example, consider
+# the following heightmap:
+
+# 2199943210
+# 3987894921
+# 9856789892
+# 8767896789
+# 9899965678
+
+# Each number corresponds to the height of a particular location, where 9 is
+# the highest and 0 is the lowest a location can be.
+
+# Your first goal is to find the low points - the locations that are lower than
+# any of its adjacent locations. Most locations have four adjacent locations
+# (up, down, left, and right); locations on the edge or corner of the map have
+# three or two adjacent locations, respectively. (Diagonal locations do not
+# count as adjacent.)
+
+# In the above example, there are four low points, all highlighted: two are in
+# the first row (a 1 and a 0), one is in the third row (a 5), and one is in the
+# bottom row (also a 5). All other locations on the heightmap have some lower
+# adjacent location, and so are not low points.
+
+# The risk level of a low point is 1 plus its height. In the above example, the
+# risk levels of the low points are 2, 1, 6, and 6. The sum of the risk levels
+# of all low points in the heightmap is therefore 15.
+
+# Find all of the low points on your heightmap. What is the sum of the risk
+# levels of all low points on your heightmap?
+
+
+from collections import defaultdict
+
+with open("files/P9.txt") as f:
+    heightmap = [line for line in f.read().strip().split()]
+
+heightmap_dic = defaultdict(int)
+for i, line in enumerate(heightmap):
+    for j, number in enumerate(line):
+        if number != "9":
+            heightmap_dic[i, j] = int(number)
+
+
+def is_low(x, y, value):
+    for neighbor in ((x - 1, y), (x + 1, y), (x, y + 1), (x, y - 1)):
+        if value > heightmap_dic.get(neighbor, 9):
+            break
+    else:
+        return True
+
+
+def part_1() -> None:
+    res = 0
+    for pos, value in heightmap_dic.items():
+        if not is_low(*pos, value):
+            continue
+        res += value + 1
+    print(res)
+
+
+if __name__ == "__main__":
+    part_1()