Brimhaven Dungeon is a multi-level dungeon located on the island of Karamja in the game Old School RuneScape. It is known for its various monsters, including skeletons, zombies, and black demons, making it a popular spot for players seeking combat experience and loot. The dungeon is accessible through a cave entrance near the Brimhaven area. Players can find resources like herbs and ore within its depths. Additionally, it features a shortcut that requires a level 30 Agility to navigate, allowing for quicker access to deeper levels of the dungeon.