Interestingly, Ireland during the 400's to 600's was something of a bastion of Catholicism and 'western/classical' thought in their monasteries. Even though Britain was very pagan and 'dark', Ireland remained 'enlightened' at this time (though the populace was still very 'dark' and pagan in Ireland).
https://en.wikipedia.org/wiki/History_of_Ireland_(400%E2%80%...
Under this regional definition of 'dark ages', even today they occur. Lost tribes in the Amazon, the populace of North Korea, very rural towns in Alaska, etc. all can be considered to be in 'dark' ages to some degree or another.