Dimensional Highways

A “dimensional highway” is a path that runs across dimensions.
Researching its history often reveals that it follows ancient straight
tracks, ley lines, etc. At points along the road, nexus portals exist. These
are usually periodic or locked, and as wide as the road itself. The road
might end at a portal in one dimension and resume at a portal in the
next – or it might continue in the original world as well, and after a
stretch, lead to another portal to a third reality, and so on. Who built
the roads? Nobody knows . . .