Manannán's castle in Lough Foyle?
I was just reading the entry in Cormac's Glossary about Manannán mac Lir - for the hundredth time. And typically, something jumped out at me that I seem to have missed before. O'Donovan (the translator) adds a note, which includes the following:
"He is still vividly remembered in the mountainous district of Derry and Donegal, and is said to have an enchanted castle in Lough Foyle."
I wonder whether he has got it slightly wrong, and is referencing the "Lough Foyle Colloquy Text" or the one about Bran son of Febal going down the well to seek treasure, but maybe not. Anybody know about this legend. References especially appreciated.