The Kiel-Holtenau Lighthouse is located at the end of the Thiessenkai, the quay on the north side of the Kiel Canal (Nord-Ostsee-Kanal), the busiest artificial waterway in the world, in Holtenau, about 12 km (7.5 mi) north of Kiel. The 20 m (66 ft) round cylindrical brick tower with lantern and gallery rising from the front of a 2-story brick Imperial-style building was built in 1895. The building includes a memorial hall, the Drei-Kaiser-Gedächtnishalle, in remembrance of Kaisers Wilhelm I, who inaugurated construction of the canal in 1887; Friedrich III, who turned the first shovel of dirt here in 1888, and Wilhelm II, who laid the cornerstone of the lighthouse in 1895. It also houses a registrar's office where weddings are performed.The traditional definitive flower series issued annually since 2005 makes people aware of the beauty and diversity of flowers in gardens and open countryside of Germany. The genus Tagetes includes about 50 species of marigolds and countless varieties in sulfur-yellow, orange or golden colors decorating gardens, parks and traffic islands. The 20¢ flower stamp (issued in 2007) depicts the French marigold (Tagetes patula), a species in the daisy family (Asteraceae).