Stoick: "Legends tell of ships that sail too close to it, only to drop off the edge of the world, never to be seen again. But those sailers who turn back tell tales of a great waterfall and dragons guarding the entrance to a hidden world."
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.
We wanted something that transcended the idea of a cave. Part of that was delving into bioluminescence and was of channeling light into this subterranean space with the use of crystals that could carry light from magma. We wanted it to be an exotic world that still feels like it belongs here on earth. But it's still a place for dragons and not for humans.
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 subterranean world contains bioluminescent fungi, as well as coral and bright crystals.
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 film.