The world is dotted with portals to the Mortal realm. Portals tend to be located along ley lines, but, since the Mortal realm does not have let lines, this is only true in the Immortal world.
Portals appear as shimmering curtains of air, usually anchored on the left and right by objects, natural or crafted. One can pass through a portal without entering it: entering a portal is an act of will. Mortals walk through portals all the time without activating them: also, they can’t see them.
Traversing a portal seems to be instantaneous to the traveler, but observation has noted the travel takes time (or that time flows differently in the Mortal and Immortal realms). Usually, a single portal transit takes 35 hours to outside observers, so a two way trip will seem almost instantaneous, but nearly week will have passed when the traveler returns.
Three portals exist on Macha, all of which emerge in the mortal realm of Los Angeles. They tend to be thematically anchored, so the portal from the Bone Garden on Macha emerges at a mortal graveyard; the portal in the seaside forest emerges between buildings by the sea, and the portal from the village emerges in a cluster of mass dwellings in Los Angeles.
Portals do sometimes emerge spontaneously, and they can cease existence spontaneously as well. This happens simultaneously at both ends. No one is known to ever have been trapped in a “closing” portal.