The brass key door doesn't open or close.
Players can clip through the walls adjacent to the brass key door while going through it.
You can clean guams at level 1 Herblore.
Level-up jingles appear in the music player.
White knights do not have a death animation. (The level 36, red-plumed ones don't, at least.)
The following music tracks do not seem to work when playing them in the music player:
Cabin Fever
The Genie
Gnome Village 2
Fanfare 2
Fanfare 3
Ground Scape
Harmony 2
Zogre Dance
Wilderness 2
Wilderness 3
Venture 2
Underground Pass
Underground
Too Many Cooks...
Tomorrow
Tale of Keldagrim
Talking Forest
Subterranea
Storm Brew
Jolly-R
Jungly 1
Jungly 2
Jungly 3
Land of the Dwarves
Mad Eadgar
Pharaoh's Tomb
Pirates of Peril
Reggae 2
Spooky 2
Brew Hoo Hoo!