The "Lost Halls" dungeon is widely considered to be the most difficult dungeon in the MMO RPG "Realm of the Mad God". It was introduced in 2017 and features new enemies, mechanics, and bosses that offer a significant challenge even for experienced players. The dungeon is designed for a group of players, and it requires excellent coordination, timing, and communication to complete successfully. The Lost Halls are also famed for their valuable loot drops, making them an attractive target for players looking for a high-risk, high-reward experience.