Things that would stand out - suspicious deaths, strange occurrences... an explanation for why a well was built in the basement, even.
Even things that don't seem out of the ordinary might be important, like who's owned the building over the years. If you don't want to tell me, I can do my own research, but I thought this might be faster.
There's something wrong with this building, and the only way to figure out what is to get an idea of its history.