Ireland - activating the crystal. 

To find this spot easily, start at the place where you exit the well, and take one step toward the white horse. Then turn around to see the tree and the wall. Hold the crystal up toward the tree until the lines turn red. They do not have to match the pattern as closely as you see in the picture here; as long as the lines are red you have found it. (Boy, doesn't that look like the outline of Michigan, flipped left to right?)

You can activate the crystal now, or wait until you have visited Maya and China as well; and do all three crystal-trips together. It doesn't matter, but there is less disc-swapping if you do them while you are there the first time.

This journey just takes you to the moon and back. Subsequent trips will be longer. You can repeat the voyage if you like.