Forgotten Realms: Splendors & Shadow
The vast, multi-leveled subterranean complex popularly known as Undermountain (or the Underhalls) has been many things over the ages — mythril mines of an ancient clan of dwarves, now vanished; a stronghold for dark elves, scheming against the light-loving peoples above; lair of untold horrors from the deep places of the world. Most recently, and perhaps for the longest stretch, it was the lair of an arch-mage of magnificent power and highly questionable sanity (two things which seem often to go together). As the legends go, he created Undermountain as both a means of safeguarding his treasures, experiments, and solitude, and as a deliberate lure for adventurers and treasure-hunters. With his magic, the Mad Mage established magical gates to bring in a wide and deadly assortment of creatures from around the world (and planes), as well as a thriving ecosystem to support them.
Over the centuries, stories of the Mad Mage faded into legend, and many began to doubt that he ever existed at all. Various powers and factions established themselves within the complex, often warring over territory and resources. Skullport, a hidden community of pirates and black marketeers, sprang up on the shores of a subterranean river, linked by magical gates to the sea above, as well as to an ocean of the lightless underworld. And the legends of riches beyond imaging continued to grow, fed by those lucky few adventurers who made it back with bulging sacks of glittering loot.
Ingress & Egress
There are a number of ways into Undermountain, but by far the most famous is the well in the common room of the Yawning Portal, an inn and tavern that’s a favorite of adventurers and mercenaries. Would-be adventurers are lowered, by way of a large iron cauldron attached to a chain hoist, and often to the traditional common room toast (“To those who went before … To those who didn’t come back!”), into the great stone well, which connects to a chamber on the first level of the dungeon; the trip down is free; the trip up costs 1 gold. Other entrances include a number of secret passages in the sewers, cellars, and catacombs of the city, as well as magical gates (some one-way or periodic) that connect the dungeons to various places throughout the city, Realms, and reportedly, even other worlds and dimensions.
The Upper Levels
Naturally, the top few levels of the dungeons (those closest to the surface) are the most well-explored, and many of the more notable features are fodder for regular tavern-talk and urban legends. Most of the physical links from the city above to the dungeons below reach the first and second levels, although a few link directly to Sargauth, the River of the Depths, and the town of Skullport, both on the third level. The uppermost level, often known as the Dungeon Level, connects in several places to the city sewers (as well as to taproom of the Yawning Portal), and is a dynamic mix of outlaw gangs from the city above, the shrines and temples of upstart and outcast cults, and monsters driven out of the deeper levels by even more horrible creatures. The next level down, sometimes called the Storeroom Level, houses many mysterious, mystically sealed vaults and chambers, said to house the Mad Mage’s failed experiments, and other things he wished to lock away. The third level down, the Sargauth Level, holds the twisting River Sargauth, and the Port of Shadow on its shores; it is also rumored to house the hidden stronghold of the Eye, a semi-legendary crime lord and slaver, whose Agents operate in the city above and throughout the surrounding lands.
Deeper & Darker
Beyond the third level, the particulars of the dungeons are less well known, and thus, more subject to wild speculation. Rumors persist of great subterranean fungus and beetle farms, whose yields sustain the complex ecosystem of the dungeons; and of a great war raging in the depths, where the dungeon passages touch the caverns of the Underdark, and nefarious dark elves clash with other creatures of the deep places. Virtually every boogeyman who has stalked the tales and nightmares of city folk and visitors is said to reside below, waiting with open claws in the darkness to devour foolhardy adventurers and naughty children.