Studio Sets and Fewer Special Effects Than You Think
Stanley Kubrick filmed and edited most of 2001: A Space Odyssey inside a studio in England, because one can't exactly fly to the moon to film on location.
At least, you'd think that'd be the reason, but Kubrick even filmed scenes he could have done on location, such as those featuring Africa, on a sound stage in England. Perhaps this was due to the director's fear of flying, but our guess is that the studio setting allowed the noted perfectionist more control than he would otherwise have.
Either way, Kubrick had to utilize seldom-used production techniques and invent entirely new ones in order to make his scenes look real.
Smoke and Mirrors
For the Dawn of Man scenes, Kubrick's people developed a rocky stage and then used a technique called front projection to provide the background of the African savanna. 2001 was "the first film to use front projection extensively, and the glow of the leopard's eyes as it sits next to its zebra kill is the result of the projector's glow reflecting off the feline's eyes" (Source).
For the interiors of the space stations and ships, Kubrick and his designers went totes ma goats on the scientific accuracy. Frederick Ordway, scientific consultant on the film, said, "We insisted on knowing the purpose and functioning of each assembly and component, down to the logical labeling of individual buttons and the presentation on screens of plausible operating diagnostic and other data" (Source). Keep in mind that this was all equipment and spacecraft that hadn't been invented yet. So it had to look authentic while having no real-life counterpart to work from. It had to look possible.
But all of this technological accuracy would be for nothing if the actors and ships didn't move realistically as well. To do this, Kubrick and his people had to devise entirely new ways of designing sets.
There are many examples of these in Kubrick and film fan circles, so we'll just focus on a few here. To start, did you ever wonder how they managed to film actor Gary Lockwood running in a complete circle aboard Discovery One?
They built a Ferris wheel-shaped set and spun the entire thing while the actor ran through it. Ingeniously, the circular set had a split through the center with flaps covering it up. This allowed the camera to be stationary while the set passed around it, and the flaps would close to cover the channel and complete the illusion. The actor had to keep pace with the set like a hamster on a wheel.
Similarly, Kubrick and his people were able to get the stewardess to appear weightless and walking up the walls by rotating the set and the camera simultaneously. (Source)
The scene where Bowman blasts his way through an emergency airlock was shot in a tall, vertical set. The camera was on the floor, and they simply dropped actor Keir Dullea, who was attached by a harness and wire that pulled him back up. The resulting freefall appears like the weightlessness of space thanks to the camera angle. Dullea has noted how grateful he was that they managed to get the shot on the second take. (Source)
Old School's in Session
2001 came before the digital effects revolution, so its special and visual effects were created without computers. The techniques used by Kubrick and his team included practical effects, such as miniatures, as well as visual effects like rotoscoping and matte shots. The filmmakers even invented new techniques such as the slit-scan shots used for the Star Gate sequence (Source). These effects won Kubrick the Oscar for best effects in 1969—the only Oscar win for the acclaimed director.
Yet, despite being a milestone in special effects, 2001 doesn't contain as many as you'd think. Its two-hour runtime only contains 205 special effect shots. For comparison's sake, the original Star Wars (1977) has 350 special effects shots, and Revenge of the Sith (2005) gets exponential on it, cramming in 2,200 such shots. (Source)