Amazing flat! In the best (in my opinion) part of Berlin, near both main train lines, Cassiopeia and fun night night an easy walk away. Flat is gorgeous, simple, and very well-maintained. Definitely want to stay there next trip to Berlin.
There are a lot of stairs, but that’s standard for Germany. Do be wary if you’re not in decent physical shape/have any handicaps. Lots and lots of stairs, which was nice for me since it burns some energy so you can pass out quickly.
One note about the key, since my travel companion messed up; leave it on the entry way table, not in the lock. I left before my travel companion and forgot to tell him, and it’s annoying for the host. Sorry again man!