This abbreviation stands for the Underworld, a place where elite player of the
world may enter. Monsters here will be Level 24+, and some monsters will even
do upwards of 200 damage! Nearly all groups will not take you unless you are
Level 20 and have some Elite Skills. Like the Fissure of Woe, you need to be
ascended before you can enter the Underworld. Underworld is a lot harder
than the Fissure of Woe, mainly because of the monsters and their damages.

To get to the Underworld, go to the Temple of Ages. Talk to the Voice of
Grenth that is in there. Talk to him, pay him 1,000g, and you will be warped
to the Underworld. You can also enter it from Grenth’s Temple in the southern-
most part of Lornar’s Pass and be warped to a different area in the Underworld
but it requires more work and isn’t worth it.

Like the Fissure of Woe, you can obtain area-specific drops in here. Most of
these items can get expensive with the right Mods. Here is a list of all the
Underworld-only drops you can get:

Globs of Ectoplasm
Eternal Bow
Eternal Shield
Storm Bow
Ghostly Staff
Demonic Remains

There is a rumor of there being Underworld armor, but the quest leading to
the crafter either doesn’t exist, wasn’t implemented, or is bugged in some
way.