Speaking with Matt Leighninger this morning I was reminded of one of my best tips for those looking for offbeat sights in Paris — the military models at the Musée de l’Armée. 
The museum is a treasure. A grande promenade stretching from the Seine leads up to the building. The courtyards are filled with captured and antique canons…hundreds of them. The canons are often works of the craftsmen’s art. Inside the museum are amazing collections of all things military stretching from earliest times to the present. There are guided tours, expositions and of course Napoleon’s Tomb adjoins the museum proper in L’Eglise du dôme. The museum is enormous and can easily occupy the better part of a day for the day.
The treat for the offbeat traveler though is in the attic. An enormous salon stretches along the right wing of the museum on the fourth level. Although the salon is often not always accessible to the public, when it is, it is well worth the trek up a few flights of stairs. In a dimly lit, attic space you will find scale models of French military fortifications and eighteenth and nineteenth century frontier towns crafted to minute detail. The feeling of the space itself is rather special, but these works of art under glass are something you will not find in such profusion elsewhere.
The model are crafted right down to pedestrians and tiny little canon emplacements on fortifications. They are lit with to appreciate a particular time of day. You will find places such as Le Rochelle, or Mayence (Mainz today). 
There are exquisitely artistic renditions of Vauban’s cutting edge fortifications utilizing bombardment deflecting glacis or redoubts that capitalise of being able to lend covering fields of fire. Even if you are not fascinated by military engineering, what you will find are true works of art in a stunning third dimension.
Although hardly a side journey, and you are probably in the locale for this in the first place, Napoleon’s tomb is awe inspiring. Resting underneath the soaring dome of the church, in a sunken arena, the red granite catafalque is only at least ten times the normal sarcophagus! The surround includes friezes representing the many civil and social accomplishments attributed to the Empire and to Napoleon. The remains of the King of Rome are also contained here, returned by Hitler during the German occupation of Paris. You will find Jerome and Joseph’s tombs in adjoining spaces along with other notable military heroes and the aforementioned Vauban. The soaring spaces and the very striking lighting make a visit to the Hotel d’Invalides a memorable experience, but you’ll find a special treat waiting in the attic of the museum if your timing is right.