+12 C (53 F) is common at nights even in the hottest month of the year (August), so be sure to take at least a cardigan, if not something that would keep you warmer.
Vangölü Ekspresi (‘Lake Van Express’) departs Istanbul’s Asian station (Haydarpasa) twice a week and arrives in Tatvan station after a 42-hr journey. This train also calls at a number of cities and towns across Asian Turkey, including Eskişehir, Ankara, Kayseri, Sivas, Malatya, and Elazig among others. Inter Rail pass is accepted in this train. See Turkish railway authority’s website.
Train station is in the upper part of the town, about 20 minutes walk away from the town centre.
Train ferries connect Tatvan with Van, a quite big city located on the eastern shore of Lake Van. These ferries accept pessengers no matter whether they have a connecting train ticket or not.
A wide highway which is in a very good condition connects Tatvan with the city of Bitlis lying 20 or so km inland from the lake.
Town's small otogar (bus station) is located on the highway to Bitlis, about half an hour's worth of walk from town centre. Dolmuşes are also available to the centre. However, most inter-city bus companies have offices in town centre, too. In fact, most otogar offices are open only during day hours, with most companies prefering to use central offices during the night.
The telephone code of Tatvan is 434 (+90 434 when calling from out of Turkey).
There is an internet cafe which costs 1.50 or 2 TL/hour, just upstairs from the ticket office of Van Gölü Seyahat bus company in the town centre.
Erzurum to the north; Malatya to the west; Diyarbakir, Hasankeyf, and Southeastern Anatolia to the southwest; Van to the east, across the lake. If you have your passport ready with a visa, why not try moving on further east to Iran?
Trains — trains to Istanbul depart twice weekly - only on Tuesdays and Thursdays at 7:10AM. If you happen to miss the train of the day, nearest station is in Batman - which has trains to Istanbul the following day (i.e. on Mondays, Wednesdays, and Fridays). Trains also depart from Batman in the morning (around 9AM). Van Gölü Seyahat has a night bus (at midnight) from Tatvan to Batman which costs 15 TL/person/one-way, arriving at Batman's otogar around 4:30AM. Walking otogar to train station take about one to one-and-a-half hour in Batman. Alternatively, you can take buses to Istanbul directly from Tatvan, but they cost more than double (70 TL/person/one-way) of what the train costs (about 30 TL/person/one-way).