We had an excellent stay at Mathieu's flat. It's very close to a metro station that takes you directly to Gare du Nord so it's perfectly located if you're coming by train or arrive at CDG. You can easily walk up to Montmartre and down on the other side and you're in the buzzing Pigalle and Planche neighborhood. We were five and fit perfectly in the flat. The collection of keys was effortless and Mathieu's lovely friend who let us in was really helpful explaining the amnesties. We'll definitely be back if we're ever in Paris.