Inner Alster covers 18 hectares and is the most prominent feature of the centre of Hamburg. It is flanked by three boulevards, the Ballindamm, the Neuer Jungfernstieg and the Jungfernstieg. The white boats, the "Alsterdampfer" depart from the Jungfernstieg for a tour across the Alster or along the canals. Outer Alster: The districts Rotherbaum, Harvestehude and Uhlenhorst border on the Outer Alster which covers 164 hectares. When the city of Hamburg expanded in the 19th century, numerous houses and villas were built around the lake. As part of the International Horticultural Show of 1953, the Harvestehude shore of the Alster and its private gardens were turned into a park. The outer Alster is a very popular place to sail yachts.