Wasserturm Hotel Cologne, Curio Collection by Hilton

Wasserturm Hotel Cologne occupies one of the city's most distinctive buildings: a restored 1872 water tower, originally the largest in Europe, converted in the 1980s into a design hotel by French designer Andrée Putman. The eleven-storey round form sets the building apart from anything else in Hilton's Curio Collection. Tapps Spa runs the wellness floor with a traditional Finnish sauna, a steam bath, and a menu of massages and body treatments, all making creative use of the tower's circular geometry. The rooftop terrace is the building's headline feature — one of Köln's best vantage points, with panoramic views over the city and the cathedral. For travelers who want a sauna inside a properly characterful Köln address rather than a standard luxury hotel, Wasserturm is the obvious option. The 88 rooms and suites pair the building's historic architecture with contemporary interior design, and the Neustadt-Nord position keeps the shopping streets, the Schokoladenmuseum, and the old town within walking distance.