"How far? Ye’ll know ye’ve found Malver’s Way when ye sees the Arch."
Gnomes, fascinated with magic, tried to find a way to safely access it, and instead wound up addicted in the deadliest way.
Thaumatechnology - in a world where straight magic has an unnerving tendency to get the user killed, either by magical catastrophe or by being lynched by an upset mob, this is a much safer form of magical use… Even if it does occasionally explode.
The extra-planar citadel of Ansern is named after its mage-founder. Ansern discovered the means to traverse the planar gulfs and created the citadel as a haven for his disciples in the art of planar-exploration. The disciples of Ansern continue his work and explore the countless worlds opened up to them by the work of the mage. They are cataloguing everything they discover in preparation for the greatest volume ever written: the Mondopedia, a book detailing many of the worlds. But the countlessness of the planes means that their book will never be finished.