One of Germany's most extensive high-altitude botanic collections, the Rennsteiggarten spreads across seven hectares of hillside with around 4,000 plant species from mountain habitats around the world. Open from May to October, it is at its most colourful in June when a blossoms festival takes place on the last weekend of the month, and again in September for the harvest festival. The garden sits right on the Rennsteig ridge, so the walk there is pleasant even before you arrive.