As the "underground" part of the name states, this apartment is in a cellar. After surprise climbs up to 6th and 7th floor walk-ups for airBnBs in Marseilles or Paris, walking DOWN one flight is a novelty.
Suitable, I think, for a single or couple for a short stay.
There's enough space for 4 people, but I don't think they would enjoy more than a day or two.