Straight tunnels are boring! Let's get groovy and ride the tube of a wavy tunnel! I printed this at 135% scale for my daughter's Guinea pigs. She will put them on the floor with the tunnel and they run back'n'forth playing in it. Think I scored some Dad points with this design.
Atomic Filament PETG
Be sure to print with 0 top and bottom shells and 0% infill!! You can print this in spiral (vase) mode, but I chose to go with 2 shells for rigidity. I think a fat 1mm nozzle in vase mode would be pretty cool!