Go Right Over
Mansions are one of the best adventure locations and most underutilized for post apocalyptic adventures around. They can be anything from a villain's head quarters to a cult's operation location.
Mansions are also tactically sound for designing adventures within.
They can also provide a DM a perfect area to deal with weird or strange areas for artifacts even as points for former state parks or as locations aboard space craft.
The real point when dealing with these types of locations for adventures is the state that they happen to be in at the time of adventuring. Are there robotic servants who maintain the grounds? Are A.I.'s still in residence as holographic presences eternally trapped within the walls of their former residence.
These locations with little work can be turned into your favorite post apocalyptic faction's headquarters. That warlord who loves his style statement pieces of his power in the post apocalyptic world or as the location for some enchanted item from the world's most popular fantasy game as a cross over point.
In the Mutant Future rpg several of these locations can be used as gonzo movie monster locations where super science has gone into overdrive.
Mutant Epoch offers a DM the opportunity to make these locations as low level encounter pieces where PC's have a great backdrop to play out all kinds of adventures and high weirdness. There are several Italian post apocalyptic movies where these place would fit in quite nicely simply add in NPC's in Roman style armor and weapons for no reason at all.
These locations can also be used for a conveying a Gothic horror or movie horror vibe without importing in any monsters at all. They're feel and influence echoes through the locations themselves. There are several articles on wiki based around these mansions so there's more then enough player handout and history available as well.
These locations could easily be ported over to games such as Lamentations of The Flame Princess and several other retroclones as dimensional traveling locations winging their way across the multiverse. This sort of story arch can be used to trap several different adventurers from various campaigns into a Ravenloft style mini campaign. Played correctly this sort of campaign could have PC's traveling through the dimensions for months.