We had a really really wonderful time staying in Karsten's apartment. Lovely interior, high ceilings to make it feel spacious even though it's small. Very powerful shower!
Absolutely fantastic location - in a quiet pretty street but so close to public transport. U-Bahn is at the end of the road (1-2 minute walk) and a few stops will take you right into the centre. Also only a 5-10 minute walk to the Berlin Wall Memorial.
Karsten was a really helpful host, let us check in and out whenever we wanted.
I'd highly recommend this place!!