Tunnels are my guys' absolute favorite thing in the world. They zoom all over, in and out, popcorning like crazy, it makes me so happy to see them having so much fun lol
I use the boxes from 12 packs of soda I just cut out the handhold part so it's big enough for them to squeeze through and open both ends. My pigs love it!
They tend to destroy it within a couple days, but it isn't hard to find more When I buy soda or I ask friends/family for their boxes. I have a small stockpile because of course they can't be without one.
Bent grids for tunnels and drain pipe. but if you get drian pipe get the pipe with the holes encase they get stuck they have lots of air until you save them. You can also cut fully across the bottom of the pipe so they never get stuck.