NASA's Neutral Buoyancy Lab, commonly referred to as the NBL, is an indoor pool that hold 6.2 million gallons of water.
This is the facility that NASA uses to teach astronauts how to perform space walks on the International Space Station (ISS) because buoyancy in the water is the closest simulation of weightlessness on the ground.
Inside of the crystal clear water of the pool are structures which represent the ISS structures and visiting spacecraft so that the astronauts can gain familiarity in this training environment before heading to space.
We were also shown high fidelity tools and what are called On Orbit Replacement Units (ORU's) that the astronauts use in training in the NBL for that same type of familiarity before they actual head unto space and perform those actions.
