Book identification - towns seperated by energy storm

Towns/cities are surrounded by a kind of swirling & confusing energy storm or field. In my mind's eye it was blue/purple in color. The towns/inhabited regions are in bubbles of normal environment.

This fantasy (or perhaps SF) world has special guides able to lead caravans between the towns/cities, without which the caravans would become hopelessly lost.

In one of the books, I think it's revealed that the energy fields between cities can charge people up with (magical?) power. I think only the guides are able to use this power.

I vaguely associate this story with Roger Zelazny but I can't find anything in his bibliography that looks like this trilogy(?).

These books would have been published no later than the late '80s.