The apartment is in a wonderful area of Paris, close to museums (Beauburg, City, Archives, etc.). Check in was remarkably easy and stress-free. The space is small, but very well planned out. It has most of what a single traveller could need to spend time in Paris. The ceiling is low, and even lower in the shower, and I could not see my son (1.83m; 6 ft 2 in) showering there without feeling cramped, and unable to wash without ducking, but ok for me (1.75m; 5 ft 9 in). I think there is heating, but no a.c. It was not necessary in mid- May. Black-out curtains were great. The flights of stairs were also fine, as the stories are low.
I agree with another reviewer that the space is a bit small for 2, but with organization it may be enjoyable.

Mirentxu is extremely responsive, gracious, and helpful through text messaging.