Lines and rectangles on the slant. I guess this could be a #VisualPuzzle.

@cliffordbeshers That looks like the sky on the other side.

@odd Yup, the innermost blue is sky.

@cliffordbeshers The structure looks like a building, not a ship or dry dock. It’s not a dam, or canyon overlook is it?

@odd It's a pretty ordinary building. There seems to be a water theme in your guesses, which is relevant, but not the way you are thinking.

@cliffordbeshers Well looking at the “porthole”, I did think about a pool too, but the tile-like concrete(?) didn’t look like it. I’m not sure where to go from here.

@odd Think "box store."

@cliffordbeshers Amazon storage/ shipping place?

@odd It's just a grocery store, but it's got a flat roof...

@cliffordbeshers With a swimming pool?

@cliffordbeshers my initial thought is a metallic cover over an electrical outlet on a wall.

@odd This prevents an unwanted swimming pool.

@dejus Much bigger than that, no electricity involved, and that's a good thing.

@cliffordbeshers Roof drain

@jomalo @gregmoore Correct! I was intrigued that @odd kept thinking it was nautical, because it is basically a scupper for a flat roofed building.