I can highly recommend staying at Cristina's place. The apartment is huge and so is the very private guest room. I was visiting Berlin for some business and didn't want to stay at another boring hotel. Cristina was very nice, basically I had all the privacy I needed but we ended up also hanging out after the work. The apartment is perfectly located 1 min walk from U Bahn, nice Kreuzberg restaurants and bars but still not too noisy. 10 min walk from Burgermeister (best burgers), 7 min from Kottbusser Tor, 5-10 min to the riverside where it's good to hang out with friends, sun & beer. Nothing negative to say, it's all good and a perfect Berlin experience with great company.