In reply to IainMunro:
The two times I've done it: The first time we started from the slopes immediately behind the hut and across a col northeast of the hut before following the valley to the top of the reservoir (frozen in winter), where there's a small ski lift and a hotel.
The second time, it was snowing heavily and we thought the slope behind the hut looked loaded, so we followed the summer road from the hut, then along the reservoir to the same spot. Less fun because it involves an undulating road and a flat traverse at the end
From there, as I recall, you pretty much have to follow the Klein Vermunt Tal to Wirl.