The former Lou’s Diner is at the corner of Leonard St. and Meeker Avenue, Brooklyn, NYC. The ’30s barrel roof diner has suffered over the years, but it is still recognizable. Some of the windows have been filled in, a flat roof has supplanted the original, and the entire thing has been painted/covered over. Despite all these changes, when you compare it to the original photograph (source), it is easily identifiable. I haven’t been able to track down any photos of the inside of the diner as it stands today, but I highly doubt much (if any) of the original components or detailing still exists.
This one’s a bit of a mystery. It’s at the corner of West End Ave and 60th St., NYC. Back in the ’20s and ’30s, this area of town was rife with diners and semi-permanent lunch wagons. This appears to be a survivor of that era, now used as an office for a parking lot. Most of these old barrel roof models has square box skylights. I think the square bump-up on the northwest end of the structure is a delete panel covering where one of these would have been.
Another possible (probable?) former diner is located at the intersection of Fresh Pond Road and Metropolitan Ave (40.712582,-73.900245) in Queens. It was formerly the Riley Diner. Here is a photo from 1949. Here is a photo of what is on that site now.