System Mechanics: Travel Between Realms:

There are more Realms to be detailed, but perhaps it is best to detail out the different ways that one may enter or travel through them, and potential benefits and consequences of each method.  First, there is the purely bystander method of peering in on a portion of the intended realm via scrying or another method of spying that does not mentally, magically or spiritually put a portion of the viewer into the realm itself.  This is the least risky, but some sights may still instill mental and emotional afflictions at a diminished amount compared to being present to see them, as well as the higher possibility that one or more other beings might be doing the same, peering in on the viewer.  Not all of them would be content merely to peer, however.  Second, the magical, mental or spiritual link to the realm via astral projection or similar method.  This allows the individual traveling the ability to see many things and pass through many things, but rarely able to directly interact with others in the realm, and some creatures and beings would be more strongly drawn to them.  Third, the magical, mental or spiritual representative body of an avatar, whether created from energy or dominating a denizen of the different realms.  This puts the most susceptibility to the individual using it as their body is relatively unguarded, but they are also visible to others and able to be hurt in the other realm.  Fourth, there is the actual physical travel into the realm itself.  This is by far the best way to ensure appropriate exploration of the realms, but at the same time the most dangerous in that those that use this method may quickly go from one realm to many others in more rapid succession, but they are also extremely vulnerable there.