Key pick up and drop off. I wish I had seen the other reviews before booking. The key pick up and drop off locations (different) were both a 28 minute walk or 18 minutes transit away. If you're going to be arriving late or departing early in the morning, save yourself the stress and *do not* book this place. The issue could've been resolved if the pick up / drop off locations were closer to the flat.
This is not Constantin's fault - he's a concierge working for the company that owns the flat. That said, the drop off location was changed at 7pm the night before check out as the initial location was closed. I responded requesting for a location closer to Gare du Nord at 10pm but he'd already logged off and didn't respond much after after my departure the next morning.
This aside, the place itself is immaculate.
Be aware only one single use packet of shampoo / body wash is provided per person. My stay was for 3 nights so we had to find out own.
Great view of Montmarte and I appreciate the washing machine.