Great location and easy to either walk or use public transport to see all that Berlin has to offer. Kreuzberg is a lively area with lots of cafes and restaurants, we really enjoyed it. The apartment itself is basic but has everything needed for a short city break and is good value for money.
There are a couple of negatives, the shower is virtually unusable, it flips from hot to cold and sprays water all over the bathroom if you are not very careful. The bath is fine as an alternative. Charlotte's communication was poor, my first message sent 4 days before arrival went unanswered for 3 days until I sent a reminder, my second message during the trip was replied to immediately and my 3rd only received a reply after I sent a reminder 24 hours later. My final message asking where to leave the key on departure still hadn't been answered by the time we left.
Two things guests should be aware of is that there are 63 steps with no lift up to the apartment. Absolutely not a problem for us but might be for some. Secondly there is no facility to store luggage after the 11.00 checkout so you need to find alternative arrangements if e.g. you have a late flight.
Overall we were very happy with our stay and Charlotte's apartment is an ideal base.