Berty's place is fantastic and located in the city center, so it's close to everything you want to see in Rotterdam. About a 20 minute walk from the central train station and around the corner from lots of cafes, bars, and restaurants. Berty was very easy to communicate with and even made arrangements with us to meet earlier in the day and drop off our luggage since we were in town so early.
The place itself is very spacious and enough for several people. It is along a busy street, so there are people walking by fairly regularly but it's a very accessible place. The apartment is very clean and Berty even left us a bottle of wine as a gift. It was a great stay and highly recommended!