Though Arthur’s grave is said to be a place of mystery, there are three sites so called.
One is in Cornwall, where Arthur is supposed to be buried beneath a stone with indecipherable letters in a nook beside the River Camel. Another, called in Welsh Bedd Arthur, is to be found amidst standing stones in the Preseli Mountains.
One famous location often associated with King Arthur’s burial is Glastonbury Abbey in Somerset, England. In the twelfth century, monks at Glastonbury claimed to have discovered the bodies of Arthur and Guenevere buried on the grounds. However, these claims are not supported by historical evidence, and the supposed graves were later revealed to be part of a pious forgery.
Source
Physical topography in Britain and elsewhere.