Both of mine like to zoom thru tunnels. Lickorish will go thru the tunnel even if its not the shortest route to the toy. Squeek will jump over or go around or thru, whatever achieves her objective faster. We left one tunnel up and Lickorish has started sleeping in it during the day now, even though she has a nice cozy heated bed not 2 feet away!
Ritz zooms in and out of the small and large ones when she is in a playing mood.
Other times, she goes half way in the small one. I think she feels safe there, like, she can see out, but no one can see her.