[QUOTE=StormArm]There is a coffin behind a door locked with an ancent key, to open it you will find the armor of comfort and a mummy will appear by the coffin.
Now if you put something into that coffin another mummy will appear, again and again, you can get full level if you have enough patience.
The exp of the mummy is very strange. When I was Lv5 wizard I can
get 188 points each, but after resting I can only get 116 points( I did not get enought exp to level up). When I level up to lv6 I can get 133 point each!!
How does it come ??

[/QUOTE]
as a wizard you can really exploit that room by placing more than one (ie 20-30+) items in the coffin, then use area blasters to...
the xp thing.
i think it works like such...
once you earn your next level (but haven't chosen it yet) nwn assumes that you take the "most powerful" option (or perhaps it defaults to ftr) and then adjusts your challenge rating, then once you have chosen your class and rested it re-calcs your challenge rating giving a slightly different score, and in some cases an improved score.