@Larry: more than a year ago I had done a map similar to your suggestion in the map ideas topic, have a look at it to see if it's OK (but it might be too big).
Still I'm sure it's easier and better to do it with the looping object, but I didn't have that idea at the time (and would need a teleport command).
edit:ok i've just done a small one, simpler and closed. Can still do another one quickly, bigger but still smaller than the first one if that's too small.
2nd edit: ok, i'm sure the second one is too small, and anyway making it is about 5 to 10minutes so... i did the medium size.
