Monster Room is a small underground room commonly referred to as a dungeon. It generates in the Overworld and is made of cobblestone and mossy cobblestone blocks. At its middle sits a spawner for zombies, skeletons or spiders. Up to two loot chests can also be found inside, typically placed near the walls.
Monster Rooms are often connected to caves, mineshafts, or other underground structures. They can appear at various heights underground and are most easily found while exploring caves or using spectator mode.
The spawner inside determines which type of mob will spawn: there's a 50% chance for zombies, and a 25% chance each for skeletons or spiders. The chests inside contain random loot, which can include items like enchanted books, horse armor, and more.
Monster Rooms can be used for setting up mob farms, collecting XP, or gathering rare loot early in the game. They're a great find for both new and experienced players looking to gear up or start a spawner-based build.