For the servants to get from place to place. There's also a nifty story for the tour guides.
I went to the Winchester
Mystery House back in 1985 when we were in the area (on the way to New
Zealand). It was my idea - I had read about it in a book somewhere, and
the idea of the house intrigued me. More than twenty years later, I
returned with my brother to the House and got the tour again; and this
time I was old enough to appreciate it.