[denysvitali]

Maybe indoors is the wrong term: as soon as you don't have direct sky visibility it's relatively hard to get a position.

Some examples: on a train, on the underground, in a train station, in a mall, in an office building, ...

[wongarsu]

Probably depends on the construction of the roof and windows. At least on European trains I've never had an issue getting GPS (unless you are in a tunnel or subway system). It takes a bit longer to get the first fix if you don't have AGPS, but no worse than in a car. Same with planes. On the other hand in a building it it pretty much only works next to a window, and malls don't have windows

[seba_dos1]

Even if you do, it will often take more time to acquire a fix than most people are used to