The castle flytrap room at the end of the game is a passage from the key room to the throne room, where Klaymen's way is blocked by a drawbridge and a bunch of spikes. The room contains, like the nursery, five hanging rings and a flytrap.
The second ring from the left lowers the drawbridge and the fourth ring from the left (second from the right) removes the spikes. It is unknown if the other three do anything. Klaymen can use the flytrap to hold down the drawbridge or the spikes, but not both at the time.
Proceeding to the pink throne room lobby requires some out-of-the-box thinking: Klaymen has to push the flytrap under the rightmost ring, jump and grab that ring, and let go. The flytrap will eat him and spit him out to the other side, into the throne room lobby.