Mario's place is great! Steps away from the Frankfurter Tor U-Bahn stop in an old, iconic building from the East German era. The Friedrichshain neighborhood is great for restaurants and bars and very close to all of the tourist attractions of Berlin by foot, bike or train.
The apartment was very clean and spacious and the kitchen had everything needed to do some basic cooking (plus a dishwasher!). Having 2 bathrooms was also an amazing amenity. I would definitely recommend Mario's apartment for anyone looking for a comfortable home base in Berlin while exploring the city.