Thor is the only god who travels through this substance instead of traveling across the Bifrost each day. In the Prose Edda, Just-As-High recounts Heimdall’s use of the Gjallarhorn to obtain some of this substance, for which he may have traded an ear. Ymir was born when some of this substance was created by the contact between Muspelheim and Niflheim. Some of this substance falls from the horns of the stag Eikthyrnir to form (15[1])(*) Hvergelmir. Some of this substance from Urdarbrunnr that turns anything it contacts white is used by the Norns to prevent decay. Odin sacrificed one of his eyes in order to obtain wisdom through some of this substance from a location named for Mimir under a root in Ginnungagap. For 10 points, name this substance found at the base of Yggdrasil in three wells. ■END■