In Watcher's Keep on Level 2 (didn't have any trouble with the Bell/Book/Can dle thing-I must be lucky)
there is a room in the center of which is a tank of Green Goo. Green Slime monsters rapidly multiply. I ran in and grabbed some stuff outof the pool and left, shutting the door on the blobs. Later I realised there must be some other item hidden in the room. Upon opening the door you can imagine my horror as I was confronted with about 25 blobs, a couple floating poison mist horrors and a 'giant snake'. It was rather academic to haste my main guy (a fighter), turn him improved invisible and then run him in the backdoor while the main party, fronted by two lesser fire elementals and a pair of Harryhousen-ized skeletons. Burst into the room to draw off the blobs. Apair of archers and stone throwers dispatched the poison mist from a distance, my fighter took out the snake and ran out with the 'key'.
The fun begins when I realized the blobs cannot damage the fire elementals and have little ability to hurt the skeletons. I literally left the room (in real life) and just left them kill blobs. I racked up a lot of XPs and amused myself with some of the only easy kills in this beeyatch of a dungeon

There are some pretty cheesey ways to get lots of XP in BG2 ;)

I agree. Like the "unlimited XP with Fire Giants in Saradush" for example.