I do think we have the ability to open up portals to other realms. The Shamans were the ones who helped people unlock the portals so they could travel to them. However, we no longer have Shamans to help us out.
I read an interesting idea from Graham Hancock who says those who experience alien abductions are really Shamans who have never been trained in how to use their abilities.
Avalon, Atlantis, Lemura (Mu) and many other locations could be physical worlds out there or other dimensions where beings visited us from or we went to visit them. (In my stories, they will be physical planets of other systems.)