diff --git a/src/AdventOfCode/Day18.cs b/src/AdventOfCode/Day18.cs
new file mode 100644
index 0000000..0efc5cb
--- /dev/null
+++ b/src/AdventOfCode/Day18.cs
@@ -0,0 +1,111 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+using System.Text;
+using AdventOfCode.Utilities;
+
+namespace AdventOfCode
+{
+    /// <summary>
+    /// Solver for Day 18
+    /// </summary>
+    public class Day18
+    {
+        public int Part1(string[] input)
+        {
+            HashSet<Point2D> points = new();
+            Point2D current = (0, 0);
+
+            points.Add(current);
+
+            foreach (string line in input)
+            {
+                Bearing direction = line[0] switch
+                {
+                    'U' => Bearing.North,
+                    'D' => Bearing.South,
+                    'R' => Bearing.East,
+                    'L' => Bearing.West,
+                    _ => throw new ArgumentOutOfRangeException()
+                };
+
+                int steps = line.Numbers<int>().First();
+
+                foreach (Point2D next in Dig(current, direction, steps))
+                {
+                    points.Add(next);
+                    current = next;
+                }
+            }
+
+            int minX = points.MinBy(p => p.X).X;
+            int maxX = points.MaxBy(p => p.X).X;
+            int minY = points.MinBy(p => p.Y).Y;
+            int maxY = points.MaxBy(p => p.Y).Y;
+
+            StringBuilder s = new();
+
+            for (int y = minY; y <= maxY; y++)
+            {
+                s.Append($"{y:D4}: ");
+
+                for (int x = minX; x <= maxX; x++)
+                {
+                    s.Append(points.Contains((x, y)) ? '#' : '.');
+                }
+
+                s.AppendLine();
+            }
+
+            Debug.WriteLine(s.ToString());
+
+            // from visual inspection, flood fill will work instead of the parity checking style from a previous day
+
+            Point2D point = (Enumerable.Range(minX, maxX - minX).First(x => points.Contains((x, 0)) && !points.Contains((x + 1, 0))) + 1, 0);
+
+            Queue<Point2D> queue = new();
+            queue.Enqueue(point);
+
+            while (queue.Count > 0)
+            {
+                point = queue.Dequeue();
+
+                if (points.Contains(point))
+                {
+                    continue;
+                }
+
+                points.Add(point);
+
+                foreach (Point2D next in point.Adjacent4().Where(n => !points.Contains(n)))
+                {
+                    queue.Enqueue(next);
+                }
+            }
+
+            return points.Count;
+        }
+
+        public int Part2(string[] input)
+        {
+            foreach (string line in input)
+            {
+                throw new NotImplementedException("Part 2 not implemented");
+            }
+
+            return 0;
+        }
+
+        private static IEnumerable<Point2D> Dig(Point2D start, Bearing direction, int steps)
+        {
+            Point2D current = start;
+
+            for (int i = 0; i < steps; i++)
+            {
+                current = current.Move(direction);
+                yield return current;
+            }
+        }
+    }
+}
diff --git a/src/AdventOfCode/inputs/day18.txt b/src/AdventOfCode/inputs/day18.txt
new file mode 100644
index 0000000..cf56975
Binary files /dev/null and b/src/AdventOfCode/inputs/day18.txt differ
diff --git a/tests/AdventOfCode.Tests/Day18Tests.cs b/tests/AdventOfCode.Tests/Day18Tests.cs
new file mode 100644
index 0000000..c8f8dec
--- /dev/null
+++ b/tests/AdventOfCode.Tests/Day18Tests.cs
@@ -0,0 +1,65 @@
+using System.IO;
+using Xunit;
+using Xunit.Abstractions;
+
+
+namespace AdventOfCode.Tests
+{
+    public class Day18Tests
+    {
+        private readonly ITestOutputHelper output;
+        private readonly Day18 solver;
+
+        public Day18Tests(ITestOutputHelper output)
+        {
+            this.output = output;
+            this.solver = new Day18();
+        }
+
+        private static string[] GetRealInput()
+        {
+            string[] input = File.ReadAllLines("inputs/day18.txt");
+            return input;
+        }
+
+        private static string[] GetSampleInput()
+        {
+            return new string[]
+            {
+                
+            };
+        }
+
+        [Fact]
+        public void Part1_RealInput_ProducesCorrectResponse()
+        {
+            var expected = 46394;
+
+            var result = solver.Part1(GetRealInput());
+            output.WriteLine($"Day 18 - Part 1 - {result}");
+
+            Assert.Equal(expected, result);
+        }
+
+        [Fact]
+        public void Part2_SampleInput_ProducesCorrectResponse()
+        {
+            var expected = -1;
+
+            var result = solver.Part2(GetSampleInput());
+
+            Assert.Equal(expected, result);
+        }
+
+        [Fact]
+        public void Part2_RealInput_ProducesCorrectResponse()
+        {
+            var expected = -1;
+
+            var result = solver.Part2(GetRealInput());
+            output.WriteLine($"Day 18 - Part 2 - {result}");
+
+            Assert.Equal(expected, result);
+        }
+    }
+}