diff --git a/src/AdventOfCode/Day23.cs b/src/AdventOfCode/Day23.cs
new file mode 100644
index 0000000..540eaa0
--- /dev/null
+++ b/src/AdventOfCode/Day23.cs
@@ -0,0 +1,110 @@
+using System.Collections.Generic;
+using System.Linq;
+using AdventOfCode.Utilities;
+
+namespace AdventOfCode
+{
+    /// <summary>
+    /// Solver for Day 23
+    /// </summary>
+    public class Day23
+    {
+        public int Part1(string[] input)
+        {
+            SortedDictionary<string, ICollection<string>> graph = BuildGraph(input);
+
+            int total = 0;
+
+            /* Look for triangles of interconnected nodes, i.e.
+
+                              node
+                             /    \
+                            /      \
+                          left -- right
+             */
+            foreach (string node in graph.Keys)
+            {
+                foreach (string left in graph[node].Where(l => string.CompareOrdinal(node, l) < 0))
+                {
+                    foreach (string right in graph[left].Where(r => string.CompareOrdinal(left, r) < 0))
+                    {
+                        if (!graph[node].Contains(right))
+                        {
+                            continue;
+                        }
+
+                        // found a triangle
+                        if (node.StartsWith('t') || left.StartsWith('t') || right.StartsWith('t'))
+                        {
+                            total++;
+                        }
+                    }
+                }
+            }
+
+            return total;
+        }
+
+        public string Part2(string[] input)
+        {
+            SortedDictionary<string, ICollection<string>> graph = BuildGraph(input);
+
+            List<string> biggest = [];
+            HashSet<string> visited = [];
+
+            foreach (string node in graph.Keys)
+            {
+                if (!visited.Add(node))
+                {
+                    // already part of another clique
+                    continue;
+                }
+
+                List<string> clique = [node];
+
+                foreach (string candidate in graph.Keys)
+                {
+                    if (visited.Contains(candidate))
+                    {
+                        // already part of another clique
+                        continue;
+                    }
+
+                    // if it's connected to every current member of the clique then it's allowed in
+                    if (clique.All(member => graph[member].Contains(candidate)))
+                    {
+                        clique.Add(candidate);
+                        visited.Add(candidate);
+                    }
+                }
+
+                if (clique.Count > biggest.Count)
+                {
+                    biggest = clique;
+                }
+            }
+
+            return string.Join(',', biggest.Order());
+        }
+
+        /// <summary>
+        /// Build the graph of every node to all the reachable nodes from that point
+        /// </summary>
+        /// <param name="input">Input edge descriptions</param>
+        /// <returns>Graph</returns>
+        private static SortedDictionary<string, ICollection<string>> BuildGraph(string[] input)
+        {
+            SortedDictionary<string, ICollection<string>> graph = new();
+
+            foreach (string line in input)
+            {
+                string[] elements = line.Split('-');
+
+                graph.GetOrCreate(elements[0], () => new List<string>()).Add(elements[1]);
+                graph.GetOrCreate(elements[1], () => new List<string>()).Add(elements[0]);
+            }
+
+            return graph;
+        }
+    }
+}
diff --git a/src/AdventOfCode/inputs/day23.txt b/src/AdventOfCode/inputs/day23.txt
new file mode 100644
index 0000000..192657c
Binary files /dev/null and b/src/AdventOfCode/inputs/day23.txt differ
diff --git a/tests/AdventOfCode.Tests/Day23Tests.cs b/tests/AdventOfCode.Tests/Day23Tests.cs
new file mode 100644
index 0000000..41c7eb3
--- /dev/null
+++ b/tests/AdventOfCode.Tests/Day23Tests.cs
@@ -0,0 +1,105 @@
+using System.IO;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace AdventOfCode.Tests
+{
+    public class Day23Tests
+    {
+        private readonly ITestOutputHelper output;
+        private readonly Day23 solver;
+
+        public Day23Tests(ITestOutputHelper output)
+        {
+            this.output = output;
+            this.solver = new Day23();
+        }
+
+        private static string[] GetRealInput()
+        {
+            string[] input = File.ReadAllLines("inputs/day23.txt");
+            return input;
+        }
+
+        private static string[] GetSampleInput()
+        {
+            return new string[]
+            {
+                "kh-tc",
+                "qp-kh",
+                "de-cg",
+                "ka-co",
+                "yn-aq",
+                "qp-ub",
+                "cg-tb",
+                "vc-aq",
+                "tb-ka",
+                "wh-tc",
+                "yn-cg",
+                "kh-ub",
+                "ta-co",
+                "de-co",
+                "tc-td",
+                "tb-wq",
+                "wh-td",
+                "ta-ka",
+                "td-qp",
+                "aq-cg",
+                "wq-ub",
+                "ub-vc",
+                "de-ta",
+                "wq-aq",
+                "wq-vc",
+                "wh-yn",
+                "ka-de",
+                "kh-ta",
+                "co-tc",
+                "wh-qp",
+                "tb-vc",
+                "td-yn",
+            };
+        }
+
+        [Fact]
+        public void Part1_SampleInput_ProducesCorrectResponse()
+        {
+            var expected = 7;
+
+            var result = solver.Part1(GetSampleInput());
+
+            Assert.Equal(expected, result);
+        }
+
+        [Fact]
+        public void Part1_RealInput_ProducesCorrectResponse()
+        {
+            var expected = 1599;
+
+            var result = solver.Part1(GetRealInput());
+            output.WriteLine($"Day 23 - Part 1 - {result}");
+
+            Assert.Equal(expected, result);
+        }
+
+        [Fact]
+        public void Part2_SampleInput_ProducesCorrectResponse()
+        {
+            var expected = "co,de,ka,ta";
+
+            var result = solver.Part2(GetSampleInput());
+
+            Assert.Equal(expected, result);
+        }
+
+        [Fact]
+        public void Part2_RealInput_ProducesCorrectResponse()
+        {
+            var expected = "av,ax,dg,di,dw,fa,ge,kh,ki,ot,qw,vz,yw";
+
+            var result = solver.Part2(GetRealInput());
+            output.WriteLine($"Day 23 - Part 2 - {result}");
+
+            Assert.Equal(expected, result);
+        }
+    }
+}