A medallion with viridian amber inlaid. Boosts maximum stamina by the utmost.
'The Erdtree's old sap becomes amber, treasured as the most precious of jewels in the age of Godfrey, the first Elden Lord.
A primordial life energy resides inside.'
These medallions, of the largest variety, were conferred to Godwyn's inner circle of distinguished golden knights.
Acquisition
It can be found in Darklight Catacombs, right after the first canon imp. Jump over on the ledge to the right and then drop down to that small archway under it.