What level is the party, and what level is the wizard?
If we are talk archmage here then I'd have the tower itself merely be a gate to an extraplanar space, ala Mord's Mansion.
Traps are killers; symbols behind curtains, etched in spell books, disintegration spells. Guardians of course litter the space from gargoyles to golems, maybe even a demon or two in "flesh-to-stoned".
False doors lead to planes, the ether, or teleport the character away, to the underdark (as far as possible underground), a tribe of giants, or even just to prision in the local town: a jail that is specially created for people who break into my tower!
All doors require passwords, or some key/symbol.
Of course, in taking on the tower information is key. The party should be able to buy, or discover some information about the tower. Others will have tried and failed. The local guild may have information, a local bard may have the tale of a rogue who died trying, a little visit to the temple of death mayallow a commune with the thief. Or maybe, his remains teleported to the local jail and his remains await the party in the graveyard... a raise dead or ressurection would provide a party member with an axe to grind. Who built the tower? Local help, planar help? All may have a little information to share...
Whatever, this is a deadly encounter.
Of course, it could just be a rouse as well. This is not the real tower. The Wizard simply enters and leaves from this place and teleports to his real tower, and this is nothing but a death trap.... hehehe....
