Skullmonkeys is the successor title to The Neverhood, which came out only on PC (and, in Japan, as "Klaymen Klaymen" on PSX). The game is an old-school jump and run type of game, with a large number of FMVs. The entire game is molded in clay.
The player takes control of Klaymen throughout the game in an attempt to put a stop to the main opponent, being Klogg, who wants to destroy Klaymen's homeworld, The Neverhood, via a huge robot called "Evil Engine No. 9". He uses an army of extremely dumb skullmonkeys to stop Klaymen in his quest; With the exception of several strange, clay birds, each and every enemy in the game is a monkey. The game features music with lyrics by Terry Scott Taylor.
The aforementioned bonus room has its own song, a lo-fi track accompanied by guitar with the lyrics written specifically for the level:
Here's a little bonus room, because I know you've had it tough.
Here's a little bonus tune, about collecting real cool stuff.
Yes, here's a little bonus room, where you can play.
Don't be frightened, don't run away.
The complete lyrics can be found in the related links section.