We had a fantstic stay at Dagmar's place. The small apartment is clean and quiet. It is situated nearby all amenities you'll need. Food, drink and transport. The Bahnhof (station) is a 3 minute walk, good coffee just around the corner and when in need for a good hamburger it's also around the corner.
A local supermarket or Lidl is...you guessed right, just around the corner.
The apartment is in a beautiful building from 1905 and has still all the architectural features (art nouvaeu/jugendstil).
Dagmar is a friendly and helpful host and when we come back to Berlin we definitely book this place again.
The nitty gritty then, the room is clean, beds are good, pillows okay, bath room clean albeit small, the apartment is located on the fourth floor (up three flight of stairs) with an own entrance to the apartment. Everything you need for a good base to explore Berlin.
And for Berlin... the city has such a variety of things to see and do, both historical or modern, that I'll do it unjust when I tell you anything. Experience for yourself and enjoy.