although Ive finished the game, I had to consult UESP to know the password for the door was 'shut up'

Just wondering where in game the player finds this out?

During the optional Concern for Nulfaga quest from Aubk'i, Nulfaga says in her usual way, during her rambling, that "I tell the door to my soul to shut up". You're supposed to be able to figure out that that's the password yourself; games back then didn't just tell you things straight out all the time, after all. She does actually tell you specifically and directly at the very end of the main quest, actually, although by then it's obviously kind of useless.

yes - and i simply love this. Seems a bit lost or at least rare nowadays...

In Arena, when you're at the Halls of Collossos, you cannot possibly solve one riddle if you have not been to one specific area of the dungeon wehre the answer lies. You do get a hint of more or less where the answer is, obviously. This kinda makes you be a real adventurer and explore everything...