Mar Baselios Cathedral is at Mount Sinai, beside the Mor Ignatius Seminary (the bishop's house) in Kothamangalam
. It was consecrated by the diocesan Metropolitan H G Thomas Mar Dionysius on 11th December, 1998. The cathedral and the seminary are situated on three acres of land, which was bought by the Kothamangalam Marthoma church
(Cheriapally) and the Mar Athanasius College Association jointly.
Among its five altars, the main one is dedicated to St Baselios Yeldho Bava. The annual feast is held on the Sunday just before the famous 'Kanni 20 Perunal' of the Kothamangalam Marthoma Church. The feast falls in the last week of September and draws a large number of devotees from all over Kerala.
Kothamangalam is about 25 km from Angamaly Railway Station