Mystara

Prime Material Plane
System:
Factions Present:	None

Mystara is not as active as Toril or Oerth in the planar sense, but it's a Prime World filled with interesting magic, particularly in a realm called Glantri and a fallen empire called Alphatia. Both have their share of gates and planar access, but most of the inhabitants are too self-absorbed to leave for long (at least on purpose).

Resource: Mystara Wiki[1]