(n) (KEY) , river, c.320 mi (515 km) long, rising near the Lake of Sils, SE Switzerland. It flows NE through the Engadine valley, then through W Austria, past Innsbruck and Solbad Hall (the head of navigation), and into S central Germany. The Inn forms part of the GermanAustrian border before entering the Danube River at Passau. There are more than 20 hydroelectric power plants on the rivers swift-flowing stream.