"I bought two of these tunnels. As soon as I set them up they each crawled in one. My one cat is a very rotund 16 pounds (he is short and squat) so he just fit in it; if he were fatter he might have trouble.
They both love the tunnels and use them periodically to hide and to play. Sometimes I pass one of the kitty teasers through the tunnel or throw a ball in and they go after it.
I do not leave them out because my cats tend to ignore things that are available all the time. So I put them out about twice per week to keep them interested.
Because of the crinkling noise my one cat always runs and gets scared when setting up the tunnel, however, she comes back to play and doesn't mind the crinkle during her play sessions. They also like the one peek-a-boo window in each tunnel.
I and my cats give this 5 stars."