And in the Led Zeppelin category, we have III with the spinning wheel that would reveal various pictures through holes in the album cover, and Physical Graffiti where the windows on the building would open to reveal stuff. And finally, In Through the Out Door where you could wipe the inside cover with a wet cloth to reveal the color.

Many albums used the large area for some kind of physical interaction. Sadly we lost that starting with cassettes.

I actually picked up an original of that album in a charity shop for 20p in about 1985. It was in mint condition, looked like it had never been played.