diff --git a/Cargo.lock b/Cargo.lock
index c0b21dc..52fce8e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -68,6 +68,7 @@ version = "0.1.0"
 dependencies = [
  "anyhow",
  "aoc",
+ "itertools",
 ]
 
 [[package]]
diff --git a/aoc2020/Cargo.toml b/aoc2020/Cargo.toml
index 58ee1cf..a5e88e4 100644
--- a/aoc2020/Cargo.toml
+++ b/aoc2020/Cargo.toml
@@ -9,6 +9,7 @@ edition = "2018"
 [dependencies]
 aoc = { path = "../aoc" }
 anyhow = "1.0"
+itertools = "0.9"
 
 [lib]
 path = "src/lib.rs"
diff --git a/aoc2020/aoc2020_bench/benches/aoc2020_bench.rs b/aoc2020/aoc2020_bench/benches/aoc2020_bench.rs
index d6a8ba8..6c9aff5 100644
--- a/aoc2020/aoc2020_bench/benches/aoc2020_bench.rs
+++ b/aoc2020/aoc2020_bench/benches/aoc2020_bench.rs
@@ -16,6 +16,7 @@ use aoc2020::day13;
 use aoc2020::day14;
 use aoc2020::day15;
 use aoc2020::day16;
+use aoc2020::day17;
 
 fn aoc2020_all(c: &mut Criterion) {
     c.bench_function("day01", |b| b.iter(|| day01::run().unwrap()));
@@ -34,6 +35,7 @@ fn aoc2020_all(c: &mut Criterion) {
     c.bench_function("day14", |b| b.iter(|| day14::run().unwrap()));
     c.bench_function("day15", |b| b.iter(|| day15::run().unwrap()));
     c.bench_function("day16", |b| b.iter(|| day16::run().unwrap()));
+    c.bench_function("day17", |b| b.iter(|| day17::run().unwrap()));
 }
 
 criterion_group! {
diff --git a/aoc2020/input/day17.txt b/aoc2020/input/day17.txt
new file mode 100644
index 0000000..2d03d2d
--- /dev/null
+++ b/aoc2020/input/day17.txt
@@ -0,0 +1,8 @@
+#####..#
+#..###.#
+###.....
+.#.#.#..
+##.#..#.
+######..
+.##..###
+###.####
diff --git a/aoc2020/input/day17_provided.txt b/aoc2020/input/day17_provided.txt
new file mode 100644
index 0000000..eedd3d2
--- /dev/null
+++ b/aoc2020/input/day17_provided.txt
@@ -0,0 +1,3 @@
+.#.
+..#
+###
diff --git a/aoc2020/src/day17.rs b/aoc2020/src/day17.rs
new file mode 100644
index 0000000..baa726f
--- /dev/null
+++ b/aoc2020/src/day17.rs
@@ -0,0 +1,110 @@
+use std::collections::HashSet;
+use std::fmt::Write;
+
+use anyhow::{anyhow, Result};
+
+use itertools::iproduct;
+
+const INPUT: &str = include_str!("../input/day17.txt");
+
+pub fn run() -> Result<String> {
+    let mut res = String::with_capacity(128);
+
+    writeln!(res, "part 1: {}", part1(INPUT)?)?;
+
+    Ok(res)
+}
+
+fn part1(input: &str) -> Result<usize> {
+    let mut pocket_dim: PocketDimension = input.parse()?;
+
+    for _ in 0..6 {
+        pocket_dim.update();
+    }
+
+    Ok(pocket_dim.points.len())
+}
+
+type Point = (i64, i64, i64);
+
+struct PocketDimension {
+    points: HashSet<Point>,
+}
+
+impl PocketDimension {
+    fn neighbours(point: Point) -> impl Iterator<Item = Point> {
+        iproduct!(-1..=1, -1..=1, -1..=1)
+            .filter(|(x, y, z)| *x != 0 || *y != 0 || *z != 0)
+            .map(move |(dx, dy, dz)| (point.0 + dx, point.1 + dy, point.2 + dz))
+    }
+
+    fn active_neighbours(&self, point: Point) -> usize {
+        Self::neighbours(point)
+            .filter(|p| self.points.contains(p))
+            .count()
+    }
+
+    fn update(&mut self) {
+        let mut processed: HashSet<Point> = HashSet::new();
+        let mut new = self.points.clone();
+
+        for point in &self.points {
+            for neighbour in Self::neighbours(*point).chain(std::iter::once(*point)) {
+                if processed.contains(&neighbour) {
+                    continue;
+                }
+
+                processed.insert(neighbour);
+
+                // if point is active
+                if self.points.contains(&neighbour) {
+                    if !(2..=3).contains(&self.active_neighbours(neighbour)) {
+                        // now inactive
+                        new.remove(&neighbour);
+                    }
+                } else if self.active_neighbours(neighbour) == 3 {
+                    new.insert(neighbour);
+                }
+            }
+        }
+
+        self.points = new;
+    }
+}
+
+impl std::str::FromStr for PocketDimension {
+    type Err = anyhow::Error;
+
+    fn from_str(s: &str) -> Result<Self> {
+        let points = s
+            .lines()
+            .enumerate()
+            .flat_map(|(i, line)| {
+                line.chars().enumerate().filter_map(move |(j, c)| match c {
+                    '#' => Some(Ok((i as i64, j as i64, 0))),
+                    '.' => None,
+                    _ => Some(Err(anyhow!("unexpected char: `{}`", c))),
+                })
+            })
+            .collect::<Result<_>>()?;
+
+        Ok(Self { points })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const PROVIDED: &str = include_str!("../input/day17_provided.txt");
+
+    #[test]
+    fn part1_provided() {
+        assert_eq!(part1(PROVIDED).unwrap(), 112);
+    }
+
+    #[test]
+    fn part1_real() {
+        assert_eq!(part1(INPUT).unwrap(), 336);
+    }
+}
diff --git a/aoc2020/src/lib.rs b/aoc2020/src/lib.rs
index f281e9a..cf569f2 100644
--- a/aoc2020/src/lib.rs
+++ b/aoc2020/src/lib.rs
@@ -16,3 +16,4 @@ pub mod day13;
 pub mod day14;
 pub mod day15;
 pub mod day16;
+pub mod day17;
diff --git a/aoc2020/src/main.rs b/aoc2020/src/main.rs
index c73812f..9c35ca5 100644
--- a/aoc2020/src/main.rs
+++ b/aoc2020/src/main.rs
@@ -18,6 +18,7 @@ use aoc2020::day13;
 use aoc2020::day14;
 use aoc2020::day15;
 use aoc2020::day16;
+use aoc2020::day17;
 
 fn main() -> Result<()> {
     let days: &[DayFunc] = &[
@@ -37,6 +38,7 @@ fn main() -> Result<()> {
         day14::run,
         day15::run,
         day16::run,
+        day17::run,
     ];
 
     aoc::run(days)