This is apartment is in a great location with easy access to the Berlin Metro. Despite being a basement apartment there is enough light for it to feel airy. There is a lack of light outside the entrance door which might not feel great when alone, although we never felt unsafe.
I would say that any more than two people would be too much and it did start to feel cramped in there. However, it’s a good base from which to just sleep and then go out and sightsee and eat in the evenings etc. Super central and you can walk to one of the central hubs in 20 minutes.
My only criticism would be for there to be basic tea and coffee supplies.
Karen is super at communication, with easy check-in and check-out and resolved an issue amicably and with ease.