Did I mention that Mercer is obsessed with concrete? Here's his house.
He built this over an old house, which he encased in concrete. (I think you can sort of see the old house he encased below.)
So unfortunately you can't take pictures inside! So Francisco took a picture of this vault decorated with tiles outside to give you an idea of what the entire inside looks like. It's almost Gaudi-esque.
Here are some other peoples' pictures of the inside:
Mercer seems like a character; his house was unlike anything I've ever seen. It was covered with engravings that he bought en masse, and cool old tiles he'd collected (including ancient tablets that in my opinion were precariously displayed). Anyway, it seems people were devoted to him--namely his assistant and his housekeeper, who he suggested marry each other later and so they did and then they kept up his house without changing a thing after his death. And they even left his clothes in his drawers until decades after his death; now they're being preserved elsewhere. (WHY?! Who needs Mercer's clothes? And why?)