I have never ever had such an amazing experience with any other hosts before. Even though my stay was longer than usual as an exchange student, Karl and his flatmates made me feel like home. The flat was very clean and tidy, with all the gadgets and equipments I needed. The location was perfectly convenient since it was very close to the Praterstern u-bahn station where you can easily find both u-bahn and s-bahn connections. Not only so, the city center is only 10mins away by bike (same for u-bahn metro). If you are planning to visit Vienna, I do not see any reasons why you are not picking up Karl's place. It is awesome!!! I guarantee you. You will definitely love all these people.