Anyone know where to get the key for the last door before the stairs at the end of level 3? the door with the gold key panel?

Also, anyone figure out the 'Spell: ???' that you get with lvl 5 Spellcraft yet?

The spellcraft spells are simply Light and Darkness, no more wasting a hand slot on torches. Not found a use for Dark yet though...

The gold key was left behind when killing a monster on level 3 (spider out of some secret room?).