Bracelet of the Deep
The Bracelet of the Deep is an artifact of Athanteen design. when worn, it makes the user incredibly resilient to water-based injury. As a result they can not drown, will not suffer from crushing weight as they descend nor will they suffer from the bends. Likewise, they are immune to temperature concerns when submerged.
It also grants the wearer perfect vision in all lighting conditions as long as they are underwater. This vision extends into the infrared and ultraviolet range.