In the Ruins of Bibracte
The mundane side of Mons Electi has a Rego-aligned Magic aura of 3.
The entrance to the regio is on the top level of the main structure of the mundane side. (It had originally been about 50 feet above the ground, before the structure was built). One enters the regio by walking around a fixed point three times in one direction. To return from the regio to the mundane side, one walks that same point three times in the other direction.
Somewhere amid the fields of sheep and woods, you can find an ornate 3 room longhut that seems to be made of a single block of stone. Here dwells Wilhelm the woodsman.