As others have mentioned, you have to be up for some serious stair climbing for this place--87 steep steps to get to the apartment, no elevator. However, you are rewarded for your efforts with this charming apartment. It is exactly as described and as it appears in the photos.
It's hard to see in the photos, but the bathroom is in the main living area, just to the right of the kitchen. The shower is completely open, the whole bath is tiled, which was unusual but worked ok. It has its own tankless water heater so it's never an issue for hot water. Some other helpful features were the hair dryer, the washer (no dryer), and the house phone for local calls. The wifi worked well throughout our trip.
Thibault's email correspondence can be a bit slow by American standards, but he was right on time meeting us and very helpful with our bags and showing us the features of the apartment.
The neighborhood is busy, and you have to be ready for drunk people yelling on the street at 3 am. It is also just steps to restaurants, and the closest Metro (Hotel de Ville) is about a 5 minute walk. It's not a quiet getaway, but if you want the heart of the Marais you can't do better. We would definitely stay here again.