The mansion must have the aspect "Hidden Passageways" cause, well, its villian hideout in an old mansion.  And as the GM, you have Fate points as well for your big bad.  The recommended amount is somewhere in the book and will be based off your party of adventures power levels.  If the PCs have had time to prepare, i don't think it is unreasonable to assume the bad guy has too.  "Traps" could be an aspect on the building that could be compeled, and the bad guy could use Hidden Passageways along wth his own aspects to simply vanish away from danger (effectively invoked to add to his defense roll, or a pre-created Veil, etc). 

It really just depends on how this villian will fight, and how he'd protect his home turf, but there are a few ideas.

Not sure that obsidian portal will help much at the table, but we use it for my dresden game and a few others and it has been wonderful for both working on a campaign as a GM and for helping to give character refreshers of what happened last session.  My group meets twice a month if we are lucky, so its been wonderful to get us right back to where we left off by writing up journals of our chars under the wiki section and the GM's adventure log, and reading them before the next session.  There are a few older games that got put on hiatus that I really wish had been put up on Obsidian so we can pick them back up easier.

You can view how we set up our dresden game at http://www.obsidianportal.com/campaigns/22034

Here are some of my favorites from brainstorming with a friend.  I've always been a fan of the saying type aspects.

"I got this."
Invoke: Wherever tackling a dangerous situation by yourself.
Compel: Player, "I could really use some help here!"  GM, "No, no, you got this."

"At least it can't get any worse..."
Invoke:  When making things worse for your opponent.
Compel: To make things worse for you.  Much worse.

"...except me."
Invoke:  There is always an exception to the rule, and you are it.  Invoke when being the exception to the rule will help you in a situation.  (A drive by happens and a bunch of people are hit with bullets ...except you.)
Compel:  When being the exception to the rule would be bad in a situation.  (A single gun shot rings out, and everyone appears uninjured ...except you.)