The Antonievo-Siysky Monastery is a Russian Orthodox monastery. It is located at the distance of 160 km from Arkhangelsk, on a peninsula of a lake, which is called Mihailovskoye Lake or Saint Lake. The Siya River (the Dvina River's confluent), which flows out of the Lake, has given the monastery its name.

The monastery was founded in 1556 by Saint Antonio, who settled on the island with some other monks. Following the saint's death in 1556, the monastery grew thanks to the salt trade with Western Europe and developed into one of the foremost centers of Christianity in the Russian North. In 1923, the monastery was closed. Both library (ancient documents and books) and treasury were taken to archives of Moscow and Arkhangelsk. The medieval buildings were used as a sanatorium and for the purposes of the collective farm, located nearby. In 1992 the monastery was given to Russian Orthodox Church. The monks returned to the monastery and started the reconstruction works. Today the monastery is open for the visitors.