PVC pipe would be the ultimate cord protector, particularly if you used 90’s to take it all the way to the outlet. As far as tunnels, you *could* use but large enough diameter pvc pipe (8 inch min even for a small bunny) isn’t usually something most people have laying around. Also, pvc is pretty slick inside. I would think a better option for a tunnel or castle connector would be concrete form tubes. They’re cheap, and places like Lowes and Home Depot stock them in 8 and 10 inch diameters. You can cut them to whatever length you need with box cutters.

I saw a pic online where a rescue used pvc pipe made into a square to keep the bunnies from moving their xpens around. I thought that was brilliant!

Concrete form tubes are large cardboard tubes that are used in construction to pour concrete into to make things like columns. Concrete is poured in and the cardboard tube is cut away once the concrete hardens. Maybe they would have them in a building supply or home improvement store there?

You could use them outdoors partially buried. That would stabilize them and give some traction for running through. Buns like to have somewhere to hang out when outdoors, so a tunnel would be great.

What diameter are they?

I think PVC is safe… Ive used rectangular PVC downpipe in the bunny room to protect the baseboards. I cut them lengthwise so I got 2 “L shape” profile lengths from each pipe. The bunnies dont even attempt to chew at it.