The Well of Forever when found in 2267 by the Excalibur.

Well of Forever is a giant mausoleum located deep within Hyperspace. Over the centuries many races have brought items to rest there for all eternity.

In 2267, Galen helped navigate the Excalibur to the location under the guise that there could be information to help counteract the Drakh plague. His actual intentions were to take the ship there so that he could leave the remains of Isabelle, his love, there.[1]

Isabelle had long believed that the Well of Forever existed, lost in Hyperspace. To celebrate her first Winter Solstice with Galen in 2258, Isabelle toasted the Well of Forever, a tradition that both her and her mother would partake in annually, with the statement, "Next year, we find it."[2]