When we were in Letterkenny a couple of years ago, we visited this theatre. They have a nice coffee cafe inside and it is quite the building.
An Grianán Theatre, with a seating capacity of 383, is the largest
theatre in Letterkenny and in the whole of County Donegal.
The theatre was named after Grianán of Aileach (‘Stony House of the
Sun’), a prehistoric ring fort located in Burt believed to date back to
1700 BC.
It opened in 1999. An Grianán Theatre website