Other forms: netherworlds
The netherworld is an alternate universe for the dead, aka hell. Sartre portrayed it as a room with annoying furniture and a quirky love triangle. On Earth, netherworld refers to a secret underworld or a no-man’s land.
In many religions and mythologies, including Buddhism and Islam, there is some concept of a world after death, a place where departed souls go. The netherworld is often deep underground, and sometimes the dead are sent there as a kind of punishment, although often it's merely a stop on the way to an afterlife. A netherworld up here is usually some seedy underworld-type situation where secret things happen. Netherworld, "place beneath the earth," comes from nether, "down or below."