Britain's Mystery Schools
On schools in Britain that were (or are) not Christian Monasteries.
Sibyl of Warinsey
Old writers refer to the Witch of Iona and the Sibyl of Warinsey on the island of Guernsey. The Norse lays of Helgi also refer to hags or sibyls on the Channel islands.
Folk tradition held that the tidal island of Mont St Michel had a college of female druids who “distributed to the faithful amulets which possessed marvelous properties and arrows which never missed their mark.” Ref : Gaels and Gauls
There is the strong possibility that mention of "crows" in many old stories is really saying "old woman/women dressed in black".
Black Madonna = Isis?
College of Theodosius / Cor Tewdws
The author of the Wiki page on College of Theodosius / Cor Tewdws starts by saying it “was a Celtic monastery and college in what is now Llantwit Major.
During the Romano-British period, some sacred sites were adopted as Mithraic temples, usually associated with a Roman military site. Others were simply called a "telesterion". One example is the Littlecote Roman Villa.
The most memorable Roman remain, however, is a stunning 4th-century mosaic depicting Orpheus, the god of the underworld, arguably the finest Roman mosaic yet discovered in the British Isles. ... The sacred site included an entrance hall with a double door to a paved courtyard. At the far end of the courtyard is a door giving access to an antechamber with a bath suite to one side and steps on the other leading to a hall with a triple apse - like a three-leaf clover design. This triple apse, or 'triconch', is unique in Britain. The hall was paved with an elaborate mosaic that survives to a remarkable degree.
Next : Ancient Time-keeping