Tentacle pool

A Tentacle pool is a pool of slimey water that can be built in an oubliette. It requires level 71 Construction, along with 100,000 coins and 20 buckets of water. When it is built, there will be a slimy pool of water in the cage of your oubliette. When challenge mode is on in the dungeon, players who fall in the dungeon will be attacked by a tentacle-like creature, and it can inflict from 0-40 life points. It cannot be attacked back. If challenge mode is NOT on, however, the player will just 'swim' in the pool.

Swimming glitch
The swimming glitch is also explained below but there is an easier method, and people usually use this method to have a swimming party where people in the house can swim everywhere. The owner of the house must build a tentacle pool in a cage and then remove the cage. (You can't build the pool without the cage in the first place). And if PvP mode is off (it doesn't work with PvP or challenge mode on), people can get dropped down the trap door in the throne room, and once they have fallen into the pool, all they have to do is simply click on the ladder without clicking anywhere else, and now you can swim anywhere around the house! The swimming glitch has been fixed, as you cannot remove the cage without removing the pool now.

WARNING: This is not an exploit and therefore the house owners activating the glitch should not be reported for Bug expoliting.

Trivia

 * There is a glitch that happens when PvP mode is off and a player is put it to the pool. When the owner of the house tells their butler to serve drink the butler will try to get in to the cage. When he gets in, the player asks him take him to the owner of the house; Which will teleport them out of the cage. The player will still appear to be swimming even though they are out of the pool. This only works if 2 players are in the home, and one of them must be the owner of the house.
 * There is a bug in the oubliette where if you attempt to drop an item in the pool, it will say: "You cannot drop items onto chairs."
 * There was also a glitch where the tentacles would appear outside the cage, and still attack players nearby.(this glitch has been fixed.)