"shouldn't" Doesn't always happen.
In Gauntlet Ledgends there was a secret level that was the Atari studio. All of the programmers, artists, etc. were skeletons colapsed over their desks and if you broke open the secret wall, the studio hampster came out and started attacking you (like a golum for those who have played it). It was worth a few experience points, but that was about it.
