"Lengthen Pegasus Seed effect"
The ring can be found inside of an underwater cave within the Sea of Storms. While in the Past at the south end of the overworld, Link can find the Sea of Storms surrounded by whirlwinds, preventing him from accessing the center. At the southwest portion of these whirlwinds, Link can dive underwater to find a single space between rocks, in which he can swim to the right and then resurface to find himself now having access to the center part of the Sea of Storms. This portion of the overworld is not accessible until after Link has completed Jabu-Jabu's Belly and acquired the Zora Scale.
When the Pegasus Ring is worn, it will increase the duration of the Pegasus Seeds, allowing Link to run for a longer period of time. This ring is useful for quickly navigating across the overworld, but it has few practical uses in the game. Even navigating the overworld has minimal effect as Link can also use Gale Seeds to quickly make his way through the overworld.