>>512988402
Yes, some aliens build a spacecraft from scratch, and some aliens hollow out an asteroid, or a moon.
Planet America's Moon has lots of underground bases, that were carved out of the rock, before the space station was brought to Earth 55k years ago.
The reason why one side of the Moon always faces Earth, is because it is a space station, and that is how space stations work.
Planet America has lots of underground bases too.
The aliens visiting us right now used to live underground, inside this planet.