Napoleon's Tomb is in the central crypt of the Dome Church at the Hotel des Invalides. You can get there by Metro. The next question is, "Why?" I went there in 1963. It's really funny -- beautiful, but funny. It's this unbelievably, over-the-top elegant space. His actual crypt is HUGE and on a raised platform in a rotunda with a dozen over-sized marble Greek-style maidens surrounding him. Around that is a balcony. You can visit either from the balcony or from the floor.
Result? Either you bow to him or you look up to him. He gets respect for eternity -- Napoleon's joke on the French people.
You can see more at: http://europeforvisitors.com/paris/photos/blg-f_paris2_invalides_napoleons_tomb_205055.htm almost 10 years ago