Arcane oozes are found in places where arcane spellcasters dwell, or in abandoned demesnes where wizards once held sway. They are encountered with alarming regularity in the depths of Sharn, the City of Towers.
The sewers are the bowels of Sharn. But there are older ruins that predate the great city. UnderSharn represents the remains of the great cities of old buried in the forgotten Depths between the LowerCity and the Sewers and the Cogs far below.
When Galifar I ordered Sharn to be rebuilt, all passages to the Depths were bound with iron and magic, and traffic between the surface and the ruins was forbidden. Still, there are many things that could draw adventurers down to the Depths. The simplest is greed. A great deal of treasure must still be hidden in the ruins of UnderSharn. In addition, a number of the dragonmarked houses had enclaves that were abandoned during the War of the Mark and lost when the city was destroyed; a dragonmarked lord could hire a party to recover relics from the past.
The Depths, or UnderSharn, is in essence a series of dungeons. The surviving sections of the city are scattered throughout the underworld, and each one may be sealed in a different manner and hold different threats.
Sharn was built on the foundations of an older city, which was itself built atop goblin ruins. This old city was destroyed by dark magic, courtesy of the elemental powers of the infamous Halas Tarkanan and his consort, the Lady of the Plague. It is said that vile powers still linger in these ruins, and for this reason King Galifar I had all the passages to this undercity sealed with gates of metal and magic. These portals remain sealed today, and it’s illegal to tamper with them. But it’s generally assumed that many treasures are hidden in the ruins of Old Sharn, along with untold secrets of the past.
No one knows exactly what lurks in Old Sharn. The ruins could contain ghosts or other undead, the vengeful spirits of the aberrant-marked people who took refuge in the fallen city. In olden times, the Lady of the Plague had power over vermin and disease, and a fanciful tale says that even today the undercity is inhabited by swarms of sentient rats and beetles.