Alysos, which is Greek for "Chains," is a giant rock that lies north of Kalambaka, southwest of the Holy Trinity Monastery and is divided northwest by a canyon ten meters deep from the rock of Agios Modestos (commonly known as Modi).
The total height of the rock is 620m. On the east side it is three hundred feet high from the base, and on the northwest side eighty. The ascent took place from the northwest side of the lower rock, with a ladder of one hundred and more steps. The entire surface of the rock accounts for fifteen acres. There was built the Holy Monastery of the Veneration of the Chains of the Apostle Peter, which the Orthodox Church celebrates on January 16th. Today it is called by the locals "Altsos" and there are few ruins.
In the early 17th century, Alysos was a Cell of the Great Meteoron Monastery. It consisted of a church, buildings, cells and stairs. In 1858 Leon Heuzey referred to Alysos as one of ten Cells at Meteora, which he learned about from local oral tradition. Bishop Porphyry Uspensky also mentioned it in 1859. Polykarpos Ramides in 1882 described it as a spacious boulder with a main church that was difficult to ascend to.
In 1977 Heinz Lothar Stutte and Dietrich Hasse climbed Alysos and told us about what they found:
"My friend found a clay jug with beautiful decor ... The jug was on a vaulted ledge of rock not far from the place where we discovered a fresco, which looked like it was hanging in a cave. Nearby there was a pile of roof tiles covered with moss and grass, which may have come from the roof of a long-ruined wooden building. On the north side of the vaulted top of the plateau were two containers carved into the rock. One was circular and had a diameter of not even two meters, while it was full of water. The other was rectangular, about the same size, and rushes emerged from its marshy bottom."
As of 1995 Alysos belongs to the Monastery of Saint Stephen.