Necklace of Adaptation

From the introduction:

For the wandering adventurer, whose travels take them to all types of harsh environments ranging from sun scorched deserts to frigid tundra to even the depths of the ocean, the necklace of adaptation is an indispensable magic item of exploration and survivability. Surrounding its wearer in a shell of breathable air, the necklace of adaptation’s creation is often attributed to the love affair between a mermaid princess and a human nobleman. But, the necklace was actually crafted during a time of war and conflict, not peace and romance, and its creation made the seas run red with blood.