The Hotel des Invalides was built by Louis XIV, for his soldiers to recover. Now, the Invalides is the burial sight of notable soldiers (such as Napoleon) and the military museum.
There is so much to see here. As well as the museum, there is the courtyard, and the chapel, and you can see the inside of the dome.
This is perfect to do whilst you’ve just seen the Eiffel Tower. From the Eiffel tower, it is a short walk to the Ecole Militaire and then to the Invalides. This area is generally really nice to walk around in.
Metro Invalides, or Ecole Militaire.