diff --git a/source/app.d b/source/app.d
index 7da990b..2298917 100644
--- a/source/app.d
+++ b/source/app.d
@@ -1,7 +1,7 @@
 import std.stdio;
 
-import day12.part1;
+import day13.part1;
 
 void main() {
-	passagePathing();
+	transparentOrigami();
 }
diff --git a/source/day13/input.txt b/source/day13/input.txt
new file mode 100644
index 0000000..5006d20
--- /dev/null
+++ b/source/day13/input.txt
@@ -0,0 +1,833 @@
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+182,648
+1014,446
+165,346
+748,228
+
+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/source/day13/part1.d b/source/day13/part1.d
new file mode 100644
index 0000000..3c36b83
--- /dev/null
+++ b/source/day13/part1.d
@@ -0,0 +1,91 @@
+module day13.part1;
+
+import std.file;
+import std.stdio;
+import std.string;
+import std.conv;
+import std.algorithm;
+import std.array;
+
+struct Point {
+    int x;
+    int y;
+}
+
+enum LineType {
+    HORIZONTAL,
+    VERTICAL
+}
+
+struct Line {
+    LineType type;
+    int value;
+}
+
+Point[] foldOver(ref Point[] points, Line line) {
+    Point[] newPoints = [];
+    void add(ref Point[] pts, Point p) {
+        if (!canFind(pts, p)) pts ~= p;
+    }
+    foreach (i, point; points) {
+        if (line.type == LineType.HORIZONTAL) {
+            if (point.y < line.value) {
+                add(newPoints, point);
+            } else {
+                int reflectedY = line.value - (point.y - line.value);
+                if (reflectedY < line.value && reflectedY >= 0) {
+                    add(newPoints, Point(point.x, reflectedY));
+                }
+            }
+        } else if (line.type == LineType.VERTICAL) {
+            if (point.x < line.value) {
+                add(newPoints, point);
+            } else {
+                int reflectedX = line.value - (point.x - line.value);
+                if (reflectedX < line.value && reflectedX >= 0) {
+                    add(newPoints, Point(reflectedX, point.y));
+                }
+            }
+        }
+    }
+    return newPoints;
+}
+
+void print(Point[] points) {
+    int maxX = points.map!(p => p.x).maxElement;
+    int maxY = points.map!(p => p.y).maxElement;
+    foreach (y; 0..maxY + 1) {
+        foreach (x; 0..maxX + 1) {
+            bool pointExists = points.any!(p => p.x == x && p.y == y);
+            writef("%c", pointExists ? '#' : '.');
+        }
+        writeln;
+    }
+}
+
+void transparentOrigami() {
+    string[] textBlocks = readText("source/day13/input.txt").strip.split("\r\n\r\n");
+    writeln(textBlocks);
+    Point[] points = textBlocks[0].split("\n")
+        .filter!(line => line.strip.length > 0)
+        .map!((line) {
+            string[] parts = line.strip.split(",");
+            return Point(parts[0].to!int, parts[1].to!int);
+        }).array;
+    Line[] lines = textBlocks[1].split("\n")
+        .map!((line) {
+            string[] parts = line.strip.split("=");
+            LineType type = parts[0][$ - 1] == 'x' ? LineType.VERTICAL : LineType.HORIZONTAL;
+            int value = parts[1].to!int;
+            return Line(type, value);
+        }).array;
+    
+    points.writeln;
+    lines.writeln;
+
+    foreach (i, line; lines) {
+        points = foldOver(points, line);
+        writefln("After fold %d, %d dots are visible.", i + 1, points.length);
+    }
+    print(points);
+}
\ No newline at end of file
diff --git a/source/day13/test_input.txt b/source/day13/test_input.txt
new file mode 100644
index 0000000..282114c
--- /dev/null
+++ b/source/day13/test_input.txt
@@ -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