A fortress shaped rock with a city on top

That's pretty much what Luxemburg is.

It's a nice city, reminds me a lot of Geneva (read very ritzy and expensive). Although, after walking around for a couple of hours, I think that's pretty much all it is, a fortress city on a fortress-shaped rock. Don't read that the wrong way, Luxemburg still rocks, home of the cheapest gas in europe!
A couple more pics here.