These tunnel tracks are intended to add a different look to your Gravitrax marble runs. I've provided 3 designs to match the standard length rails. I've printed mine with eSUn PLA+ green, which is fairly close match for the Gravitrax green. The models are printed without supports. You may need to use a small file to remove any strings or small blobs on the inside of the tunnel.

I designed these after I discovered that a similar design on Printables has been taken down and would have provided a link to that person's work. 

So these were built from scratch.  Mine are inspired by the the Sound Tunnel near Jeff's Zipper in Melbourne.