Players can build the Rocnar, flame pit, and spikes without a cage. However, it is impossible to remove/upgrade the cage without also removing its contents. The tentacle pool still needs a cage to be added. It is not possible to voluntarily step into a cage, and therefore the tentacle pool is unsuited for players who desire to use the oubliette as a way to kill themselves quickly (restoring all stats).
To hold players dropping from a throne room above. Players have to pick the lock (using Thieving) of the gate, or force the lock (using Strength) of the gate, to get out. The stronger the cage, the harder it will be for players to escape. If a player tries to enter the cage voluntarily (for example by attempting to pick the lock from the outside) the game will stop them.
It is possible to kill the tentacles in the tentacle pool with the help of a summoning familiar, the tentacles will drop bones on death.
One of the traps players can add is called a "Rocnar", which when spelt backwards becomes "rancor". This was a monster in Jabba the Hutt's oubliette from Star Wars episode 6, which tried to kill the protagonist Luke Skywalker.
The hanging skeleton requires two skulls to build, although there are four hanging skeletons in the room.
When you rest in the flame pit, the recurring damage doesn't interrupt your resting. However, elsewhere in RuneScape if you were to take damage while resting, your resting would be interrupted.