The experiment cave is a cave involved during the quest Creature of Fenkenstrain. It can be accessed by pushing the easternmost grave to the south-east of Fenkenstrain's Castle. During the quest, players have to kill a level 51 experiment to obtain the cavern key to the northern gate in the cave.
The cave is the only place in RuneScape that contains experiments, and the level 25 experiments are often killed for combat experience. Due to the easy combat experience for both high and lower levels, the cave is frequently crowded.