The thing I’m calling a monument was the configuration of clay tiles in a diamond pattern and a stone tile in the middle, or sometimes stone flooring around one stone wall. Maybe it was a coding error for a house, but it definitely looked like something. Sometimes found in caves, or randomly on the beaches. I don’t have a screen shot, and really don’t feel like looking for one right now. But they didn’t do anything, and probably won’t exist in the next version, so I wouldn’t spend a lot of hours losing sleep over it.