Joachim's place is close to the S train station and conveniently placed from the city center with around 15-20 min train ride depending where you want to go. Also around 20 min bus ride to the airport.
There are many nice bars and cafes around Charlottenburg too if you need a german breakfast before exploring the city.
The place was clean and quiet, with everything found as presented in pictures and Joachim was very helpful in providing directions and advice. Also, the way the place is decorated is a truly immersive experience with many pieces of history that you'll discover while exploring Berlin :)