Hidden World

"It's a hidden dragon world!"

- Hiccup

The Hidden World is the major and titular location that will be featured in the upcoming How to Train Your Dragon: The Hidden World.

Official Description
"The Hidden World is an old sea-faring legend about a land at the edge of the world, where many sailors have lost their ships - never to be seen again. Those who have returned reported sightings of a great waterfall and dragons guarding the entrance to a hidden world beneath the sea. A land from which all dragons hail."

- Dean DeBlois

Geography
Dean DeBlois confirmed that the Hidden World is located within a massive volcanic caldera that serves as a gateway to an endless maze of chambers and tunnels, which in turn work their way around the world.

This underground world contains bioluminescent fungi, as well as coral.

Trivia

 * The Hidden World is a famous myth/legend from the distant seas. It is sometimes called "a world beyond the sunset".
 * The Hidden World appears to be an incredibly ancient location due to how massive the stalagmites and stalactites are. This is because rock formations take billions and billions of years to grow just half of the size of the ones that are shown in the trailer.