Lucid dreaming is the doorway to visiting others. It can be somewhat difficult to become a Lucid dreamer. You can access higher functions and States once your Lucid. Then after that you may or may not be able to access others. This all depends on their mental capacity as well. Like if they have a natural mental defense it can be quite difficult to access them. If they have none it could be quite easy. But nonetheless dream States are fun regardless.