Vincennes is not technically located within any of the 20 arrodissements of Paris (it's just to the east), though to walk its streets you'd never know you had left the city proper. Still, this small distinction is likely the only reason why such an incredible structure, constructed by Charles V in the 14th century and added to 300 years later by the Sun King himself, has managed to escape the throngs of tourists that descend upon the French capital by the millions each year. Lucky you. Instead of standing in lines or straining your neck for a view, you'll likely have the place to yourself (ok, there may be a couple dozen other people there).
And just what is there to see? Well, there's the magnificent cathedral (entrance is a small additional fee, but well worth it), the formal gardens (parterre) and the massive, 52 m tall main tower. This behemoth alone is worth the visit, which saw not only the death of England's young King Henry V but also the 18th century imprisonment of the marquis de Sade (among other notable figures). You can even read hand written letters he composed during his captivity displayed in his cell. So consider skipping the crowds for a day to come experience a remarkable piece of unsung history in a city not known for its hidden cultural gems.