The key that opens the way to Eureka.
Eureka Key is a key item, which is required to open the way to Eureka, an area located within the Crystal Tower that houses the most powerful weapons. It can be obtained by defeating Doga and Unei at Doga's Grotto
A key found in a faraway world that opens the way to the Forbidden Land, Eureka. It is said that there are weapons and magic beyond the control of mortals that lie in wait there. Equipping this key will increase magic and spiritual power, and boost resistance against fire, water, wind, and earth attacks.
Eureka Key is an accessory that provides 20 MAG, 20 SPR, and +20% resistance to Fire, Water, Wind, and Earth. It is obtained by completing the Hard version of the Final Fantasy III event, Doga's Grotto.