Take a hike to Germany's highest alpine lake with an island on 1813 m / 5949 ft! From the saddle, you can cross the border to Austria. The duration of this hike is 7-8 hrs total for a day trip or you can make it an overnight (bivy). The trail is well signposted and is predominately grass, mud, and loose rock.
Lake Schrecksee lies squeezed in the Bavarian Alps and is well signposted from the trailhead. Especially during summer this location is popular as a swim in the alpine lake will cool you off!
To get there drive towards Hinterstein in the Allgaeu region. Follow the small main street until there is a large car park at the end. Leave your car (make sure you pay the fee) and follow the signs for 'Hinterbachhof '. Follow the restricted road for easy 20 minutes until you reach a power house on your left. The trailhead is after crossing the bridge on your left at coordinates 47.454759, 10.438807. It's actually signposted, but the sign is a little hidden and you have to climb over a fence. From there it's a contentious uphill hike.
The area is used for cattle during the summer months so either bring enough water or bring a purifier.
There are far more hikes and it's recommend to go up the saddle to get an overview of the area. The saddle marks the Germany - Austria border.
Note: Officially it is not allowed to camp up there. German law only allows to bivy. Thus it's really important to leave no trace and never leave your gear unpacked during there day.