Danube conservation and touristic development of the Danube region. In medieval Regensburg, with its maintained old town, stone bridge and cathedral, the Route of Emperors and Kings begins. It continues to Engelhartszell, with the only Trappist monastery in Austria. Further highlight-stops along the Danube include the "Schlögener Schlinge", the city of Linz, which was European Capital of Culture in 2009 with its contemporary art richness, the Melk Abbey, the university city of Krems and the cosmopolitan city of Vienna. Before the Route of Emperors and Kings ends, you pass Bratislava and Budapest, the latter which was seen as the twin town
Danube an important industry. The Upper Danube ecoregion alone has about 60 fish species and the Lower Danube–Dniester ecoregion has about twice as many. Among these are an exceptionally high diversity of sturgeon, a total of six species (beluga, Russian sturgeon, bastard sturgeon, sterlet, starry sturgeon and European sea sturgeon), but these are all threatened and have largely–or entirely in the case of the European sea sturgeon–disappeared from the river. The huchen, one of the largest species of salmon, is endemic to the Danube basin, but has been introduced elsewhere by humans. Important tourist and natural spots along the Danube include