North-east of Kastri is the imposing gorge of river Tanos, where the Monastery Timiou Prodromou is built on an abrupt rock in the 12th century. Due to its inaccessible location, it was used during the revolution in 1821 as a resistance base against Ibrahim and a shelter during his raids. Its water mill was grinding gunpowder during the revolution. It was the only monastery that survived the siege by Ibrahim's troops, who besieged the monastery twice without succeeding.