Ahch-To was an uncharted world, located in the Ahch-To system within the Unknown Regions of the galaxy, positioned at the coordinates F-13 on the Standard Galactic Grid. Ahch-To orbited twin stars, including the second sun. In turn, the planet was orbited by one moon. The planet supported a breathable atmosphere. The world shared a mysterious time-related quality with such locales as Mortis and Dagobah.

Due to the the planet’s great distance relative to its twin suns, Ahch-To supported a temperate and damp, but volatile climate that frequently caused salt spray, cold winds, and violent storms, unlike the desert world of Tatooine. Ahch-To also experienced summers, autumns, and winters.

The surface of the planet was nothing but deep blue oceans. Dotting the oceans, however, were volcanic island archipelagos formed of black rock that were covered with few green trees and grass.

The rugged cliffs of Ahch-To’s islands were home to moss, grass, and ferns. An algae flourished in the seashore pools. Two Force-sensitive plants, the uneti trees—native to Ahch-To—and uneti shrubs, were found on the planet. Fragrant flowers, nightkelps, reed, and the seaweed also grew on the planet.

Ahch-To was the homeworld of the Lanai, an avian sentient species, and of a large variety of creatures, such as birds, fish, sea mammals, and great leviathans of the deep, with gulls and frondtrailers among them. Small, flighted porgs nested in colonies along the cliffs, feeding their young with regurtiated fish and Ahch-Tonian grubs. A species of chirping sticklike insects inhabited the hardy grasses, while others flew in the air.

Several species of fish inhabited Ahch-To, the edible ones such as fingerlip garpon, twinfin hyacander, and spetan channelfish, coppergrin, billfish, needlegawp, while others included tytahuso fish and an unidentified fish.

There were larger creatures, such as the pallaskean sea-serpents that inhabited the oceans, the wharlithans, and the thala-sirens that nursed their young on the rocky shores, providing a dairy source for other island residents.