Every environment in Sea of Thieves is the result of a huge collaborative effort between many different members of Rare's multidisciplinary team. For over 2 years I've served as an environment artist on the level art team which means my main responsibility was to shape the natural world of the game and populate it with assets created by our world artists and outsource partners. No one artist usually owns an environment or an asset completely, so huge credit to the fantastic team at Rare!
The Ancient Isles hold secrets and riches long forgotten in its dark caves and dense jungles. These islands are generally more vertical, a lot denser and lush while still enjoying a tropical climate.
My main contributions to this area were rock formations on Thieves' Haven, Plunder Outpost, Discovery Ridge, a couple of smaller islands that later became skeleton forts (natural base only) and helping define placement density and lore themes for riddle voyages.