Not much to go on but I've kept looking for years, hope someone can help.
About 25 years ago I bought a second-hand book from a camp site shop in the UK. It was about a man transported to an alien planet/alternate dimension, possibly from a building site? He finds a green woman and a form of transport that is a floating black object, possibly a cube. I remember the cover looking quite old.
The only further thing I can think of is that I think the cover had a blonde man on it with a silly long bowl cut (think He-Man) and a green woman with a black bob. I bought the book early 90s and I think it was probably 60's or 70's. It was in English. I've racked my brain and searched Google for years but never got anywhere. I don't know why I keep searching as I clearly can't remember the book well!