Short answers, pulled from the story.
The Inn is 518 kilometers long. It rises in the Swiss Alps west of St. Moritz, flows northeast through the Austrian state of Tyrol and its capital Innsbruck, then runs north and east through Bavaria before joining the Danube at Passau.
The Inn carries a larger average discharge than the Danube at their confluence in Passau, but the Danube is classified as the main river because it has a greater total length, drains a larger surface area, and maintains a more consistent flow.
The name Inn derives from the old Celtic words en and enios, meaning water. The double-n spelling appeared in the 16th century, with the Tyrolean Landreim of 1557 as an early example, and the short-vowel pronunciation has been standard since the 18th century.
On the 3rd of June 2013, the Inn reached a discharge of 6,820 cubic meters per second at Passau and a water level of 12.85 meters, the highest recorded flood level at that location since 1501. The historic centre of Passau was severely flooded.
There are 24 hydroelectric power plants on the Inn, of which 17 are operated by Verbund AG. They range in capacity from 4.3 megawatts at Islas near the headwaters to 288 megawatts at Pradella.
The Engadine is the valley of the Inn in the Swiss Alps, named after the river. The Romansh form is Engiadina and the Latin was vallis Eniatina. It is the only Swiss valley whose waters drain to the Black Sea, via the Danube.