The Tomb of Scathach

The Archdruid and Spearmistress Scathach was a hero from the Nysian Rebellion that died in the Age of Legends. According to rumor, she was interred in a grove that she had been cultivating since before the Rebellion began.
Originally part of a pilgrimage for aspiring Druid's, over the Ages, her tomb sank into the Clearwater Lake.
Many have tried to make it to the lake bottom to discover if the structure there is actually the Tomb of Scathach, and retrieve her Divine Regalia.
As yes, none have survived.