We were met off the train at Alexanderplatz by Steffen, this was a great bonus as our first visit to Berlin. He walked us to the apartment block (5 mins max) and handed over the keys. He also text us a few recommendations later on that was really kind.
The Sky cabin was exactly as described - great view and made of concrete. Comfy bed - bigger than expected. We loved it as our little sky cabin for the weekend.
It is in a brilliant location, we walked or hopped on trains and trams everywhere.