Space

Space is a void-like area about 1000 blocks above sea level. You can build up to it, but be careful... there is no air and if you get up too high, there is no gravity and you cannot fall back down.

How
The higher you get, the less gravity there is, and the higher you jump. If you jump too high your oxygen bar will appear as if you are underwater.

Tips
You can make a space station in space itself, or on a moon. Niether have oxygen, and while space has no gravity, Moons only have reduced gravity.

Use an Oxygen Generator to fill your sealed space station with breathable air.

Use Mag Boots to stay on a space station. Only works with iron or iron lining!