Les Invalides began as the army hospital, initiated by Louis XIV in 1670 and finished six years later. These days, it is a complex of buildings including a collection of museums, a hospital and retirement home for war veterans, and a chapel which is a burial place of war heroes including Napoleon Bonaparte. The museums include Contemporary History, Maps, as well as Military History.
As is the way with French Kings and their projects, a simple idea to build a place for war veterans to retire grew into a massive and grand statement with fifteen courtyards, a chapel - the Eglise Saint-Louis des Invalides, and then a royal chapel - Eglise du Dome. Based on St Peter's Basilica in Rome, this latter became the prime example of French Baroque architecture.
Les Invalides is easy to reach. Take metro line 8 to Invalides, or 13 to Varenne or Saint Francoise-Xavier or RER C to Invalides station.