I'm convinced that chickens see tunnels as amusement park rides, I've never seen a chicken not use a provided tunnel.
I'm in the process of building a "chook play ground" that will have at least two tunnels attached to a cube for them to play king of the cube on. There will also be a swing and teeter totter. I got the idea for these "toys" from watching chickens in with goats, the chickens were playing with the same "toys" the goats played on and with, except for the swing, that is a fairly standard chook toy.