I must have passed this disc, in the sidewalk on the north side of Elizabeth Street between Regent and Clemens, hundreds of times, and yet I’d never noticed it before. For some reason I stopped to look at it this time, thinking it was a groundwater well cover. To my surprise, it is something cooler (at least if you have my temperament): a survey monument, specifically a benchmark.

I don’t know much about survey monuments, but this one seems plainer and less informative than ones I have stumbled on elsewhere. I wonder what is hidden beneath the lid? It appears to be open up if a screw is removed. I also don’t know what the code on the rim means.