I'm a fan of the Grande Bibliothèque, and often consult its Iris catalogue. But here's a weird thing: that link goes 404 at night. I'm not sure what their closing time is, but this is the only internet resource I've ever encountered that closes at night, and they don't even put up a page saying so. It just disappears off the web, plain old 404 Not Found.

If there's some arcane update that has to be done nightly, they could at least put up a page explaining this and saying when the service isn't available. But it's the nature of web resources to be open 24/7 and it should ideally be available all the time.
posted at 20:57