Here’s the idea: Imagine traveling in a large circle and taking four photographs along the way. After developing the photos, you get them out of order. Could you put them back in sequence on the basis of the spatial relationship of the structures you had passed?
Okay, now that you have the idea, check out “I Took a Trip on a Train” and see how you do.
(Go to http://www.learner.org/teacherslab/math/geometry/space/train/index.html.)