xyzzy

A hollow voice says...

A hollow voice says 'PLUGH'.

Nothing happens.

...but for a moment, you smell damp limestone
and hear the echo of dripping water, as if
standing in a colossal cave far underground.

The feeling passes. You're still in Ghelmyon.

(Colossal Cave Adventure, Will Crowther, 1976.
 The game that started it all.)