"The apartment is on the third floor."
Translation:La apartamento estas en la tria etaĝo.
The problem I have with this is that most of the time when an american says the "third" floor that means to an Esperantist the "dua etaĝo".
Esperanto is a lot more literal than English. You're not on the train, you're in the train. The apartment is not on the third storey, it's in the third storey.