Well of Urd

The Well of Urd is a magical well, that appears in the Norse part of the Fall of the Trident campaign in Age of Mythology.

Overview
After the heroes manage to prevent Gargarensis from accessing the Greek entrance to Tartarus, and a ressurected Osiris destroys the entrance from Abydos, Gargarensis tries to free Kronos by travelling far north, to Midgard, from where he can descend to Niflheim, the Norse Underworld, and breach the third gate to Tartarus.

Niflheim, one of the Nine Worlds in Norse mythology, is accessible via the Well of Urd. In order to pursue Gargarensis and stop his plans, the heroes must first reach it, this being the main focus of the eponymous The Well of Urd mission.

Its second appearance is in the Beneath the Surface mission, where the player must defend the Well of Urd from the enemy's attemps to destroy it, as the Well is the sole passage for reinforcements, as the player starts descending to Niflheim. In this mission, the Well acts as an Underworld Passage between Midgard and Niflheim, so units can be transported between the two lands.

Mythology
"Known also as the Well of Fate (Urdarbrunnr), and guarded by the Norns; this is one of three wells providing water to Yggdrasil, or the World Tree. The Well of Wisdom (Mímisbrunnr), guarded by Mimir; and the Hvergelmir (Roaring Kettle), the source of many rivers, are the other two. All three wells lead to the realms of Asgard, Jotunheim, and Niflheim, which are located deep in the underworld."

- In-game help section