Considering the Ferrotel Duisburg in Duisburg?
A VT member wrote the following comment about visiting Duisburg:
Botanical Gardens on the Kaiserberg by Weissdorn
Near the University of Duisburg on the Kaiserberg, they have some lovely botanical gardens. The gardens have been here since 1890, and are around 195 hectars, with a garden section, an herbal garden, a national plant bed, an ecological section, and even rare plants and flowers from the Alps and the dunes. There is no charge for visiting the garden yourself. If you want a guided tour, you should call the number below. The gardens are open everyday all year long from 8 a.m. until sunset. The best time to visit the gardens is in May.