He was the reputed founder of
Llanrwst and his festival, known as
Gwyl Rwst, is held on 1 December. The site of Grwst's original cell or
Llan is now occupied by the Seion
Methodist Chapel in Llanrwst, with the nearby Cae Llan housing estate the location of the first church dedicated to him by the 11th century. An annual fair was held on these grounds during the 16th century to celebrate the saint's feast day, with the area known as
Gwgrwstw after him. ==References==