There are decent hostel-style dorms above the Zur Muehle restaurant in a very good location just off the town centre...also a HI hostel in Obertraun on the far side of the lake...
You won't be stuck for places to explore...eg, you could spend the best part of a day just walking around the lake, stopping off here and there...also there is a funicular which takes you up the mountain directly behind the village where you can have a drink or a meal at Rudolf's tower and then head off on one of the trails...or take the boat across the lake and then head up to the Dachstein ice-caves and afterwards ascend to the summit of Krippenstein mountain where there is a very good hut/restaurant and walks in several directions...
The tourist office in town can supply you with info and maps for walks etc...