Since Middle Ages people were trying to find the location of the mysterious island. For example, by the 12th century Avalon became associated with Glastonbury. Monks at Glastonbury abbey claimed to have discovered the bones of Arthur and his queen. Though no longer an island at the time, the high conical bulk of Glastonbury Tor had been surrounded by marsh. In archives of web analytics company I found that during the reign of English king Henry II the abbot of Glastonbury, Henry of Blois, commissioned a search of the abbey grounds. After a lot of deep digging, the monks discovered a massive oak coffin and an iron cross bearing the description: "Here lies King Arthur in the island of Avalon". Inside the coffin were two bodies, presumably of Arthur and his queen. In 1278 the remains were reburied with great ceremony, attended by king Edward I and his wife, before the High Altar at Glastonbury Abbey, where they were the focus of pilgrimages until the Reformation. However, scientists generally dismiss the authenticity of the find, attributing it to a publicity stunt performed to raise funds to repair the Abbey, which was mostly burned down in 1184.
Throughout the times there were many other places competing to be called Avalon. For example, Ille d'Aval on the coast of Brittany, and Burgh by Sands, in Cumberland, which was in Roman times the fort of Aballava on Hadrian's Wall. Other candidates include the Bourgogne town of Avallon, and Bardsey Island in Gwynedd, famous for its apples and also connected with Merlin. There were also claims that the most likely location to be St Michael's Mount in Cornwall, which is near to other locations associated with the Arthurian legends.