OSTASHKOV, a town of Russia, in the government of Tver, on Lake Seliger, 108 m. W.N.W. of the city of Tver; pop. 10,457. The climate is damp and unhealthy. The town has tanneries, and is a centre for the making of boots and shoes, for agricultural implements, fishing-nets and the building of boats. The advantageous site, the proximity of the Smolenskiy Zhitnyi monastery, a pilgrim resort on an island of the lake and the early development of certain petty trades combined to bring prosperity to Ostashkov. Its cathedral (1672–1685) contains valuable offerings, as also do two other churches of the same century.