Ethereal Travel

The Ethereal Travel spell is perhaps the most unusual of all of the spells of Thaumaturgy.

It allows the caster to travel to the Ethereal Void, seemingly the only way to leave the world of Pagan. Where exactly into the void the caster teleports to however, is not determined and can be greatly influenced by outside forces. Also, the requirements for this spell are quite steep, as Blackrock is a substance very difficult to find on Pagan, since it is extraordinary rare.

Note also, that unlike other spells, the "reagents" are not used up when charging the spellbook, meaning that the rare substance is not lost to the caster.

Generally, casting it on Pagan leads to the Ethereal Plane, the home of all four Titans, who won't allow anyone to escape their world in this way. That however also leads to them being vulnerable in that place.

Trivia

 * The spell can only be bought after reading the book about the Tongue of Flames from Malchir and the book Mythran summons after speaking to him about it, then telling him to recreate the obelisk. That also blocks purchase of all other Thaumaturgy spells.
 * Note that it isn't necessary to actually buy the spell from Mythran. An alternate way to cast this spell is to find a pentagram, as it is used for binding spells in Sorcery, and place the blackrock objects at the five points where usually the reagents are (as seen on the picture on the right). Then double-click on the obelisk tip to teleport to the Ethereal Void. If some of the fragments disappear, they were placed correctly (don’t worry, they are automatically returned to your backpack). If some don’t, they were the ones whose placement you must correct.