We were there at the restaurant. Nice place, delicious food. The atmosphere is gorgeous. And the price is the most important thing - very affordable for such a place! I advise everyone, it's better than obscure eateries in Berlin.
Great hotel. But if possible, take a room with a view of the city. Overlooking the aquarium is of course beautiful. But it's always dark. It is not clear day or night. And it's very stuffy. But everything is fine in the room. The breakfasts are excellent.
At a time of high workload, the staff becomes boorish. The hotel has not been renovated since it was built (it feels like). Tiles are falling off in the spa pool. The spa is open from 6 am, but the sauna starts to warm from 9. * I highly recommend hydro massage in the pool, cool to break tired leg muscles after walking.
Breakfast for 3+. Everything seems to be there, but the choice is not like 5*.
Excellent location of the hotel: across the bridge is Museum Island, on the other side is Alexanderplatz. There is an amazing multi-storey aquarium inside, so take a room with windows inside.