Saw it when it premiered in 1968. In 70mm Cinerama.
The moon and Jupiter sequences looked 3-D in 70mm.
I've seen it in re-releases on standard movie screens and you just have no idea how much less you're seeing. Shame that Cinerama didn't stick around.
I saw it in re-release when I was in 8th grade, which would have been '74.
The theater was a Cinerama theater.
The same theater is also where I saw Logan's Run, Star Wars, Close Encounters of the Third Kind, Alien, Escape from New York, Flash Gordon, Battlestar Galactica, Buck Rogers, Return of the Jedi, Big Trouble in Little China, Terminator, Aliens...
I miss the River Hills Theater.