What's the Title of This Haunted House Book?

Long ago I read a haunted house book published in the 1970s (or perhaps much earlier?). I don't remember the title. 

A group of people gathered to investigate a haunted house. They thought that some rooms might be sealed off. So they hung towels from every window, then checked from outside to see if any windows had no towels (indicating the door to that room had been walled up and hidden from them).