If you're re-doing the map from scratch, then there's a number of things you might want to include. Winding tunnels are an absolute must, without too many open areas, and the monsters will have to be positioned carefully. I never liked the cave levels in Hexen where the monsters were scattered all over the shop.
The ruined temple is a class idea, and I can just imagine how you'd have to fight your way through, backtracking when the roof has caved in, finding holes in the floor (IF we get the engine to handel it [img]images/smiles/icon_wink.gif[/img] ) to jump through between the various levels...
What you might want to include is a Thief-style underground forest scene, with greenery and such growing in a very "magical" kind of way. It would add a very surreal, very authentic touch to a game that heavily involves magic.
Anyway, that's just a thought.