My boyfriend, his 7-year old son, and me stayed at Maarten's place for 1 night. The old house is beautiful, with a big garden in the front. Perfect for a bonfire, to which we were warmly invited upon arrival. The rooms were cosy, warm and stylish, with lots of Donald Ducks for the little one ("Can't we stay longer, please?") and a all the amenities you need.
Our stay was unfortunately too short to enjoy the beautiful surroundings and Maarten & Juliane's hospitality to the fullest, but we would love to come back in spring or summer for part 2. We are very curious to see what the results of the renovations are by then!
If you are traveling by public transport and plan to walk: S-Bahn station Griebnitzsee is the better choice, not Wannsee. It's a 20-25 minute walk, but if you're lucky you can also take a bus and walk only 10-15 minutes. Or tell Maarten in advance and he might be able to pick you up.