Zugspitze (2962 m) is the highest peak in Germany. It lies south of the town of Garmisch-Partenkirchen, and the Austria–Germany border runs over its western summit. South of the mountain is the Zugspitzplatt, a high karst plateau with numerous caves. On the flanks of the Zugspitze are three glaciers, including the two largest in Germany [wikipedia].
This route is one of the easiest route to Zugspitze but you have to be very fit to be able to do it one day. Unlike many other routes it does not require climbing equiment.
Statistics: elevation gain 2460m, 500m descent, 21.1km distance, about 5hrs in total.
Ascent: The hike starts from the train station "Ehrwald Zugspitzbahn". You walk for about 50mins through the village to the "Ehrwald Almbahn Talstation", continue to "Ehrwald Alm". TBD, see the GPS track
Descent: Take the Austrian (not the German one to Garmisch!) cable car back to Ehrwald. Usually it operates till 16:40 (with some special events sometimes till 21:30). Walk down the "Ehrwald Zugspitzbahn" (about 35mins) or take the bus, if it still operates.