This is not a vortex tunnel. When I worked at Netherworld so many seasons ago, there was a tunnel in the clown area (downstairs). It was the first time I had seen a tunnel used for anything that wasnít specifically built for children in an outdoor park. Since then, I have seen them and even removed them from other haunts. But, if you didnít know, my black book of ideas started when I worked there. The tunnel inspired this idea:
The Spinning Crawling Tunnel
There is a round hole in the wall that leads people into a tunnel. As they crawl through, the tunnel begins to sway back and forth. The further they crawl through the more the tunnel rotates and even spins all the way around.
Picture this as a blending of the fun house tunnel and the crawl tunnel. The difference is there are no motors. This tunnel is moved by the active people inside it (or a near-by actor). This tunnel should not be made of concrete like those in the fun house. I am not sure what you will end up using but please make sure you pad the inside. Additionally, the floor at the end of this tunnel should also be cushioned.
In the drawing, I simply drew out the idea, much like the pictures. There are none of these made that I know of yet so there are no measurements.