Waterdeep:Undermountain
Over a thousand years ago, the wizard Halaster Blackcloak journeyed from far away to what is now known as Mount Waterdeep. With seven apprentices at his side, he used his magic to summon mighty beings from other planes to build a wizard's tower to dwarf all other wizard's towers. He dug deep into the mountain, eventually reaching the Underhalls, a mithral mine abandoned by the Melairkyn clan dwarves, where drow and duergar had taken up residence.
Using his new underground Undermountain complex as a base of operations, Halaster collected strange and dangerous creatures from other planes and from distant lands with which he populated his dungeon. The Undermountain became Halaster's obsession, and he spiraled into madness. Those of his apprentices who stayed by his side were not spared his fate.
Over time, Halaster's tower fell into disrepair and then into ruin, and then Waterdeep was constructed in the shadow of the mountain. The early settlers sent criminals into the depths of the Undermountain as punishment, for none returned alive. None, that is, until the adventurer Durnan ventured into the Mad Mage's lair and returned with riches aplenty. He used his newfound wealth to destroy what remained of Halaster's tower and build an inn in its place.
A knot in the Weave
Before Waterdeep, and before Halaster, the ancient elven city of Aelinthaldaar stood here, capital of the elven kingdom of Illefarn. When the elves left, they used powerful magics to erase all traces of their capital city. As a side effect of their casting, they created a knot in the Weave underneath the mountain.
This snarl sometimes causes madness to one degree or another in the minds of mortals, which usually manifests as an obsession with the mountain and what lies under it. It is, in fact, the source of Halaster's madness, and the obsession of the Melairkyn dwarves before him. This is even the reason Durnan braved the hazards of the Undermountain, and why he remains in the area. Not all who dwell in the Undermountain succumb to the madness caused by this tangle of magic, but any who spend a considerable time below the surface risk falling victim to it.
The Yawning Portal
The Yawning Portal inn was constructed on the site of Halaster Blackcloak's tower, and the well leading into the Undermountain still remains as a centerpiece in the tavern floor. Durnan constructed the inn after his first foray into the Undermountain, and runs the inn today.
Adventurers who hang around the Yawning Portal often find work venturing into the Undermountain on errands for others.
Undermountain secrets
There are many secrets you can uncover about the Undermountain. Some you can learn by just listening in on patrons in the Yawning Portal, while others you may need to discover within the dungeon of the Mad Mage itself.
Alterations to magic
- No spell other than wish can transport someone into or out of the Undermountain, or to travel from one level to another. Entering and exiting must be done by more conventional means, and traveling between levels must be done via conventional means, or via the gates that Halaster has created for that purpose. Astral projection, teleport, plane shift, word of recall, and similar spells, when cast for this purpose, simply fail. Similarly, any spell which would banish a creature to another plane of existence will fail. Any properties of magic items, even artifacts, are subject to the same restrictions.
- Despite technically being a different plane, magic that transports a creature to the Border Ethereal, such as the etherealness spell, works as expected. However, any venture into the Border Ethereal that begins within the Undermountain and attempts to end outside it will cause the creature to be pulled back into the Undermountain. Similarly, entering the Border Ethereal outside the Undermountain and attempting to leave it within the dungeon will cause the creature to be ejected.
- Magic that temporarily summons creatures or objects from other planes works normally within the Undermountain, as does magic dealing with extradimensional spaces. Spells that are capable of permanently summoning a creature from another plane (such as conjure elemental) fail. Any spells cast within an extradimensional space (eg, magnificent mansion) that was accessed from within the Undermountain is subject to all of the same restrictions as spells cast within the Undermountain.
- Spells cannot destroy or alter the shape of the Undermountain's magnically protected ceilings, walls, floors, pillars, or columns. For example, earthquake would not trigger a ceiling collapse or create fissures in Undermountain. Doors and furnishings, however, are not protected in this way.
- Characters who receive spells from deities or otherworldly patrons continue to do so within the Undermountain. Spells which contact beings from other planes function normally.
Elder Runes
Elder runes are ancient symbols imbued with magical power. With years of study, any creature that can cast the symbol spell can learn an elder rune and add it to the selection of symbols that can be created with the spell. Halaster has spent lifetimes studying elder runes, inventing new ones, and harnessing their volatile magic. He likes to place them throughout Undermountain as hazards.
Each Elder Rune has a beneficial (boon) and detrimental (bane) effect associated with it. The caster who inscribes the rune can choose which effect to apply when the rune is triggered, or have the effect be chosen at random.
Gates
Halaster has constructed a number of magic gates throughout the dungeon. Most gates permit travel from one floor of the dungeon to another, although some allow for ingress or egress from the Undermountain.
Opening a gate requires a key, though "key" in this case can be more metaphorical; some keys are the casting of a specific spell, or performing some specific act. Legend lore or similar spells can reveal what the key for a gate is, if no other means of learning the information is available.
Gates typically stay open for 1 minute, although wish can force one to stay open for up to an hour. A gate cannot be opened if it is within the area of an antimagic field, though if such a field encompasses an open gate, it will stay open for its duration. Dispel magic has no effect on gates. A gate cannot be damaged or destroyed except by wish.
Elder Runes on Gates
Every gate Halaster has constructed contains an Elder Rune. Usually, but not always, the rune will affect the first creature to step through an open gate. Once an Elder Rune on a gate has triggered, Halaster must personally refresh the rune before it can be triggered again.