We spent three nights in Charles' lovely apartment in Montmartre. As Charles was travelling himself, his brother handed over the keys and kindly explained everything to us.
The apartment is perfect for a couple and the neighbourhood is really nice - we enjoyed especially the cheese shop and the bakery around the corner.
We slept very well though I guess in colder seasons the old house can become a bit cold (but of yourse there are radiators).
We can definitely recommend it!
And: thanks a lot for the map and the yummy chocolate!