For all cultures, the Underworld is the land where the spirit of mortals go to after their death. Hence the name, it is located beneath the Earth's surface from which it is accessible through a handful of passages and sunlight is absent.
The presence of stalagmites indicate that water may be seeping through the ceiling. The ground is mostly rocky in appearance with large skeletons embedded within while cliffs are typically pitch black. It is presumably a very hot environment due to the presence of magma rivers and pools. However, Erebus has shown to be able to support flowing water that form rivers. Few plants and animals can survive in Erebus.
The dominant flora consists of pine trees, known as dead pines, who have been stripped of their leaves. Fauna consists of Wild Boars, Harpies and Serpents, the latter of which will attack intruders without provocation. All three types of Underworld may be interconnected as Myth Units from various cultures appear in all three. Erebus and Nifelheim both have Tartarus located beneath them as they are shown to have Hades Gates leading to it.
The Greek Underworld is the realm of the god Hades. It is the only one where flowing water is seen.
Residents of Erebus consists mainly of the many variants of Shades but true Myth Units also appear, including Minotaurs, Cyclopes and Leviathans. Erebus has two random maps based on it, namely Erebus and River Styx. In the Fall of the Trident campaign, two passages to Erebus exist, one near Ioklos in Greece and another in Egypt.
The most notable feature of Nifelheim is the presence of the Taproot that grow from the great tree Yggdrasil. The Nidhogg is also said to dwell in Nifelheim, constantly gnawing at the roots of the tree.
The most notable passage into Nifelheim is the Well of Urd, which can safely transport units from the surface into Nifelheim without harm. After Thor sealed the Hades Gate, an explosion caused part of the surface to cave in, exposing the world below.
Diyu has corkscrew shaped plateaus, upon which rests relics or other treasures. As of the Tale of the Dragon campaign, it is the only place where Griffons have been seen. The primary residents however are Jiangshi who live alongside Shades in a Forgotten City.
Diyu is apparently an unpleasant location, as Yama claims that anyone who enters is just another victim to be tortured. Diyu has two known passages, one of which leads to the East Sea in an area not far from Ao Kuang's palace.
The Underworld appears in the following campaign scenarios.
Fall of the Trident Edit
- Revelation (Erebus)
- Strangers (Erebus)
- Good Advice (Erebus as a dream)
- Beneath the Surface (Nifelheim)
- Unlikely Heroes (Nifelheim)
Tale of the Dragon Edit
- The Realm of the Dead (Diyu)
- Despite being underneath the Earth's crust, being in the Underworld does not prevent the use of God Powers that revolve around the sky such as Rain and Eclipse.
- Underworld Passages do exist in Egypt as seen in the Fall of the Trident campaign, but its version of the Underworld has never been seen.