Also known as the fjord of the Alps, Achensee's clear blue green waters lie between the steep sides of the Karwendel mountain range in the west and the Brondenberg Alps in the east. The beautiful, serene lake is the largest in the Tyrol region, being 9.4 km (5.8 mi) long by 1 km (0.6 mi) wide with a depth of 133 m (436.3 ft). The cool water is so pure and clear that it is almost drinkable and possible to see to a depth of 10 m (32.8 ft).
Lake Achen's position in the valley means there is often a brisk wind on the lake, giving ideal conditions for sailing and windsurfing. There are boat trips up and down the lake, starting from the main tourist centre on the shores Pertisau. Pertisau is also right on the edge of the Karwendel nature reserve, the largest protected area in Europe. Here, it is possible to hike along designated trails, experience fixed rope routes and possibly spot the chamois or ibex that make their home in the forests of these spectacular limestone and dolomite peaks. In the winter you can take a funicular or gondola up the skiing areas at Zwolferkopf, or near Muracham Aachensee. In summer, the more daring traveller can try paragliding.
For a panoramic view of this dramatically beautiful lake there is a hike up to the top of Barenkopf. But to sit back and enjoy the scenery without too much effort, try the steam railway from Jenbach up to the lake. Near Aachensee there are popular bathing and picnic spots, although the lake’s water is a little cool for swimming.