Well, for dream walks and spiritual journeys and whatnot, it would kind of depend on what tribe and what type of magic and whatnot. Some times, there have been 'meditative journeys' around the world which demand a person on Earth to bring the person back in time to not die or whatever (because they'll likely starve to death if left to their own devices).

And, if you're planning to have Merlin travel the world, just weave the Kama Sutra in. He finds out, and throughout your lovely story, every time he and/or Arthur need a specific type of clarity of mind, they consult the Kama Sutra for help. ^_^

Also: NO! I have too many things to do as is!