There are a couple of indoor locations that you can fast travel directly from, without having to go outside first. Railroad HQ is one such example.

However most buildings require you to get outside first, which can be a pain - especially if you are returning to the same spot multiple times as part of quests.

Why the difference? I would have said a cell loading limitation, but again RR HQ (and at least a couple other interior locations) avoid it. (?)

I can think of only 3 that support fast travel to interior locations. cannot explain the choices except to balance the type of travel that any given player prefers: Walking, FT or VertiBird rides.

It would be nice to fast travel in and out of the Prydwen...

Also on the subject...anyone notice that if you fast travel to Diamond City, and Diamond City Market...it puts you like 20 feet apart from each destination? Why not if you choose Diamond City, it places you outside? SMH...