On a budget, Les Invalides & Napoleon's Tomb still earns its price.
€15 (free under 18 / EU under 26)
The gilded dome is a landmark in its own right, and beneath it Napoleon lies in a grand red-quartzite sarcophagus. The Musée de l'Armée is comprehensive — a lot for military-history buffs, a bit much for everyone else. The dome and tomb alone are worth the stop.