By far the most interesting monument in Paris, with its 3 levels of cryptes, its dissymetrical tours and the incredible labyrinth of galleries, staircases, attics and rooms which the usage is sometimes rather hard to determinate. One detail however; several people live in this church, so the exploration must be done in silent... not to disturb.

If most of the monuments are visitable it's unfortunately never in their entirety or at the best time. With luck, a scaffolding could compensate for this inconvenience. If not it only remains for you to be a good acrobat or to manage on your own to get the keys.