A base in the middle of the Atlantic ocean with a very tall fictional skyscraper (scenarios included)
It scales to a height of 64,000 metres which is the edge of space. It is open spaced inside with 2600 floors and a few walkways scattered in several places. Deltagliders can takeoff or land from inside and taking off vertically without hitting any walls or walkways can be quite challenging.
I attempted to make this building higher but Orbiter seemed to cut off visually for base structures i.e. blocks, hangars, beaconarrays etc. after 64,000 metres so this was the highest I could realistically go.