Check out these cylindrical grinding images:
Image by Travis S.
These are obviously ground stone tools. As for what the two biconical stones are on the left, I have no idea. Maybe they had boat lines wrapped around them.
The piece at the top looks like it might be part of a pipe.
Cylindrical space station
Image by verysubmm
Really it’s my 360 degree Niagara Falls panorama converted to polar coordinates with the GIMP, but it reminds me of a painting commissioned to depict the inside of a city-sized cylindrical space station, sort of like Babylon 5, but with sunlight coming in one end.
No, a rainbow wouldn’t really look like that; it’d still be circular.
Inspired by those Little Prince type planetoids people are making, but easier since the source panorama doesn’t need to include the ground (i.e. directly down).