I have a house piggie called Winston and I have hung toilet roll inners from the top of the cage and stuffed them with hay - he loves to reach and strecth up for his hay. He also has the cheese cube block things stuffed with hay as well. they love hiding in things, and running in and out of bigger tubes. Also paper bags with hay etc in.
I hide Winston;'s veggies in the toilet roll inners and also in the cubes, so he has to forage for his food.....
pampered piggies is a great website, with lots of brilliant ideas.
Good luck!