Nemrut Dağı (3050m), rising to the north of Tatvan, is an inactive volcano with several crater lakes. (Note that this is not the more famous Nemrut Daği near Malatya.) From the crater rim (13km from the main road) you get sensational views over Lake Van, Tatvan and nearby water-filled craters. You can also hike to the summit (about 45 minutes) from the rim – just follow the lip of the crater (the last stretch is a bit of a scramble).
Midweek, your only company will be shepherds with their flocks and sturdy sheep dogs. Follow the dirt road from the crater rim leading down to the lake and find your own picnic area. Visits are only possible from around mid-May to the end of October; at other times the summit is under snow.
A taxi from Tatvan is around ₺150 return. On summer weekends hitching is an option.
With your own transport, leave Tatvan heading to Bitlis, and turn right at a sign saying 'Nemrut 13km'. At the time of writing, this rough road was being resealed for improved access. You'll then reach the crater rim, from where a dirt road winds down into the crater and connects with other dirt roads snaking around the crater.
Guided trips can be undertaken with Alkans Tours in Van.