Neutral buoyancy is one of the main ways weightlessness can be simulated on earth. To accomplish this, underwater versions of spacecraft, robots, and spacesuits are built.
Flotation is added until the hardware is just light enough to neither sink nor float.
Then, when underwater, it behaves as if gravity had no effect. Interestingly, people are naturally nearly neutrally buoyant, which is why they can swim. It is the only one located on a college campus and the only one dedicated to basic research. Here is a picture of what is currently happening in the neutral buoyancy tank. The NBRF also houses other facilities.