oubliette

In the centre of the chamber there is an oubliette to the darkness below.

It was an oubliette—a pit with a trap-door, which drew the veil of oblivion over the man who had vanished.

In this there used to be in olden times an oubliette in which unhappy prisoners were let down.

It was an oubliette, a dungeon where the prisoner might be buried alive, and never come forth again, alive or dead.

As he plunged into the deep water of the oubliette a fiendish laugh echoed in his ears.