diff --git a/2021/day13/Cargo.lock b/2021/day13/Cargo.lock
new file mode 100644
index 0000000..74e24a1
--- /dev/null
+++ b/2021/day13/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day13"
+version = "0.1.0"
diff --git a/2021/day13/Cargo.toml b/2021/day13/Cargo.toml
new file mode 100644
index 0000000..36c9510
--- /dev/null
+++ b/2021/day13/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "day13"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/2021/day13/README.md b/2021/day13/README.md
new file mode 100644
index 0000000..f3f41f9
--- /dev/null
+++ b/2021/day13/README.md
@@ -0,0 +1,169 @@
+https://adventofcode.com/2021/day/13
+
+## \--- Day 13: Transparent Origami ---
+
+You reach another volcanically active part of the cave. It would be nice if
+you could do some kind of thermal imaging so you could tell ahead of time
+which caves are too hot to safely enter.
+
+Fortunately, the submarine seems to be equipped with a thermal camera! When
+you activate it, you are greeted with:
+
+[code]
+
+    Congratulations on your purchase! To activate this infrared thermal imaging
+    camera system, please enter the code found on page 1 of the manual.
+    
+[/code]
+
+Apparently, the Elves have never used this feature. To your surprise, you
+manage to find the manual; as you go to open it, page 1 falls out. It's a
+large sheet of [transparent
+paper](https://en.wikipedia.org/wiki/Transparency_\(projection\))! The
+transparent paper is marked with random dots and includes instructions on how
+to fold it up (your puzzle input). For example:
+
+[code]
+
+    6,10
+    0,14
+    9,10
+    0,3
+    10,4
+    4,11
+    6,0
+    6,12
+    4,1
+    0,13
+    10,12
+    3,4
+    3,0
+    8,4
+    1,10
+    2,14
+    8,10
+    9,0
+    
+    fold along y=7
+    fold along x=5
+    
+[/code]
+
+The first section is a list of dots on the transparent paper. `0,0` represents
+the top-left coordinate. The first value, `x`, increases to the right. The
+second value, `y`, increases downward. So, the coordinate `3,0` is to the
+right of `0,0`, and the coordinate `0,7` is below `0,0`. The coordinates in
+this example form the following pattern, where `#` is a dot on the paper and
+`.` is an empty, unmarked position:
+
+[code]
+
+    ...#..#..#.
+    ....#......
+    ...........
+    #..........
+    ...#....#.#
+    ...........
+    ...........
+    ...........
+    ...........
+    ...........
+    .#....#.##.
+    ....#......
+    ......#...#
+    #..........
+    #.#........
+    
+[/code]
+
+Then, there is a list of _fold instructions_. Each instruction indicates a
+line on the transparent paper and wants you to fold the paper _up_ (for
+horizontal `y=...` lines) or _left_ (for vertical `x=...` lines). In this
+example, the first fold instruction is `fold along y=7`, which designates the
+line formed by all of the positions where `y` is `7` (marked here with `-`):
+
+[code]
+
+    ...#..#..#.
+    ....#......
+    ...........
+    #..........
+    ...#....#.#
+    ...........
+    ...........
+    -----------
+    ...........
+    ...........
+    .#....#.##.
+    ....#......
+    ......#...#
+    #..........
+    #.#........
+    
+[/code]
+
+Because this is a horizontal line, fold the bottom half _up_. Some of the dots
+might end up overlapping after the fold is complete, but dots will never
+appear exactly on a fold line. The result of doing this fold looks like this:
+
+[code]
+
+    #.##..#..#.
+    #...#......
+    ......#...#
+    #...#......
+    .#.#..#.###
+    ...........
+    ...........
+    
+[/code]
+
+Now, only `17` dots are visible.
+
+Notice, for example, the two dots in the bottom left corner before the
+transparent paper is folded; after the fold is complete, those dots appear in
+the top left corner (at `0,0` and `0,1`). Because the paper is transparent,
+the dot just below them in the result (at `0,3`) remains visible, as it can be
+seen through the transparent paper.
+
+Also notice that some dots can end up _overlapping_ ; in this case, the dots
+merge together and become a single dot.
+
+The second fold instruction is `fold along x=5`, which indicates this line:
+
+[code]
+
+    #.##.|#..#.
+    #...#|.....
+    .....|#...#
+    #...#|.....
+    .#.#.|#.###
+    .....|.....
+    .....|.....
+    
+[/code]
+
+Because this is a vertical line, fold _left_ :
+
+[code]
+
+    #####
+    #...#
+    #...#
+    #...#
+    #####
+    .....
+    .....
+    
+[/code]
+
+The instructions made a square!
+
+The transparent paper is pretty big, so for now, focus on just completing the
+first fold. After the first fold in the example above, `_17_` dots are visible
+- dots that end up overlapping after the fold is completed count as a single
+dot.
+
+_How many dots are visible after completing just the first fold instruction on
+your transparent paper?_
+
diff --git a/2021/day13/input/example0 b/2021/day13/input/example0
new file mode 100644
index 0000000..bc63ff8
--- /dev/null
+++ b/2021/day13/input/example0
@@ -0,0 +1,2 @@
+Congratulations on your purchase! To activate this infrared thermal imaging
+camera system, please enter the code found on page 1 of the manual.
diff --git a/2021/day13/input/example1 b/2021/day13/input/example1
new file mode 100644
index 0000000..282114c
--- /dev/null
+++ b/2021/day13/input/example1
@@ -0,0 +1,21 @@
+6,10
+0,14
+9,10
+0,3
+10,4
+4,11
+6,0
+6,12
+4,1
+0,13
+10,12
+3,4
+3,0
+8,4
+1,10
+2,14
+8,10
+9,0
+
+fold along y=7
+fold along x=5
diff --git a/2021/day13/input/example2 b/2021/day13/input/example2
new file mode 100644
index 0000000..4a6d6fe
--- /dev/null
+++ b/2021/day13/input/example2
@@ -0,0 +1,15 @@
+...#..#..#.
+....#......
+...........
+#..........
+...#....#.#
+...........
+...........
+...........
+...........
+...........
+.#....#.##.
+....#......
+......#...#
+#..........
+#.#........
diff --git a/2021/day13/input/example3 b/2021/day13/input/example3
new file mode 100644
index 0000000..eb2caa0
--- /dev/null
+++ b/2021/day13/input/example3
@@ -0,0 +1,15 @@
+...#..#..#.
+....#......
+...........
+#..........
+...#....#.#
+...........
+...........
+-----------
+...........
+...........
+.#....#.##.
+....#......
+......#...#
+#..........
+#.#........
diff --git a/2021/day13/input/example4 b/2021/day13/input/example4
new file mode 100644
index 0000000..8d475a3
--- /dev/null
+++ b/2021/day13/input/example4
@@ -0,0 +1,7 @@
+#.##..#..#.
+#...#......
+......#...#
+#...#......
+.#.#..#.###
+...........
+...........
diff --git a/2021/day13/input/example5 b/2021/day13/input/example5
new file mode 100644
index 0000000..bfcca03
--- /dev/null
+++ b/2021/day13/input/example5
@@ -0,0 +1,7 @@
+#.##.|#..#.
+#...#|.....
+.....|#...#
+#...#|.....
+.#.#.|#.###
+.....|.....
+.....|.....
diff --git a/2021/day13/input/example6 b/2021/day13/input/example6
new file mode 100644
index 0000000..d59120b
--- /dev/null
+++ b/2021/day13/input/example6
@@ -0,0 +1,7 @@
+#####
+#...#
+#...#
+#...#
+#####
+.....
+.....
diff --git a/2021/day13/input/input b/2021/day13/input/input
new file mode 100644
index 0000000..556b07a
--- /dev/null
+++ b/2021/day13/input/input
@@ -0,0 +1,812 @@
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+977,432
+711,399
+12,628
+
+fold along x=655
+fold along y=447
+fold along x=327
+fold along y=223
+fold along x=163
+fold along y=111
+fold along x=81
+fold along y=55
+fold along x=40
+fold along y=27
+fold along y=13
+fold along y=6
diff --git a/2021/day13/src/main.rs b/2021/day13/src/main.rs
new file mode 100644
index 0000000..d9ce07f
--- /dev/null
+++ b/2021/day13/src/main.rs
@@ -0,0 +1,81 @@
+use std::collections::HashSet;
+use std::io::stdin;
+
+fn main() {
+    let mut buffer = String::new();
+    let stdin = stdin();
+
+    stdin.read_line(&mut buffer).ok();
+
+    let mut points: Vec<(i32, i32)> = Vec::new();
+    let mut instructions: Vec<(char, i32)> = Vec::new();
+
+    // parse points
+    while !buffer.is_empty() {
+        // parse
+        let mut numbers = buffer.trim().split(',').map(|s| s.parse().unwrap());
+        let x = numbers.next().unwrap();
+        let y = numbers.next().unwrap();
+        points.push((x, y));
+
+        // read next
+        buffer.clear();
+        stdin.read_line(&mut buffer).ok();
+
+        if buffer == "\n" {
+            break;
+        }
+    }
+
+    stdin.read_line(&mut buffer).ok();
+
+    while !buffer.is_empty() {
+        let instruction = buffer.trim().split(' ').nth(2).unwrap();
+        let mut parts = instruction.split('=');
+        let axis = parts.next().unwrap().chars().next().unwrap();
+        let line = parts.next().unwrap().parse().unwrap();
+        instructions.push((axis, line));
+        buffer.clear();
+        stdin.read_line(&mut buffer).ok();
+    }
+
+    println!("Points: {:?}", points);
+    println!("Instructions: {:?}", instructions);
+
+    let part1 = apply_instructions(&points, &instructions[..1]);
+    let part2 = apply_instructions(&points, &instructions);
+
+    dbg!(part1.len());
+
+    let width = *part2.iter().map(|(x, _)| x).max().unwrap() + 1;
+    let height = *part2.iter().map(|(_, y)| y).max().unwrap() + 1;
+
+    for y in 0..height {
+        for x in 0..width {
+            if part2.contains(&(x, y)) {
+                print!("#");
+            } else {
+                print!(".");
+            }
+        }
+        println!();
+    }
+}
+
+fn apply_instructions(points: &[(i32, i32)], instructions: &[(char, i32)]) -> HashSet<(i32, i32)> {
+    let mut translated_points = HashSet::new();
+
+    for point in points {
+        let (mut x, mut y) = *point;
+        for (axis, line) in instructions {
+            if *axis == 'x' && x > *line {
+                x = 2 * line - x;
+            } else if *axis == 'y' && y > *line {
+                y = 2 * line - y;
+            }
+        }
+        translated_points.insert((x, y));
+    }
+
+    translated_points
+}