The Experiment cave is a popular combat training area. The area is exclusive to those who have started the Creature of Fenkenstrain quest. It can be accessed by entering the tombstone south-east of Fenkenstrain's Castle. One must push the eastern-most memorial to enter. The cave is filled with experiments which accounts for its popularity, as the experiments have very low Defence and high Constitution, allowing players of all levels to acquire large amounts of combat experience in a relatively short space of time. Players who have completed the quest cannot train on the level-51 horse-like experiments, because they will get a message: You don't have the heart to kill this poor creature again. Note: This will occur as well if a player has a cavern key in his/her inventory. If this is the case, the player can drop the key and be able to kill the monster again. However, there is really no reason to.
The cave is usually flooded with players on popular worlds, but barren in less popular worlds. When the caves are flooded, players may try to secure agreements with other active players on who gets to kill which monster to avoid kill stealing.