I think it's one way figuratively- for people. They're not going let someone go back and forth on a whim, but they can probably send back something with messages. Now that I think of it, I don't know how this would be done. However we have to remind ourselves that we only saw the pilgrimage happen from the perspective of the main character who was super stressed and he ran through it right before it was supposed to close and then he was really disoriented. So maybe there's a gate going the other way and there's a chance to throw something in it.