One of the best ways to keep your guinea pig amused is to provide her with something to do (as well as eating, [pooping] and sleeping of course...) - a good idea is to provide her with tunnels and things to run through (so she can daydream and pretend she is running through little trodden down pathways in the grasslands of South America...) - Cardboard 'Chubes' (above) from petshops are ideal for them to hide in and nibble.

Piggies love to go in and out of things so you can either buy your pig one of the 'pigloos' available in petshops or get a variety of cardboard boxes / shoe boxes which you can cut openings in (make sure you don't leave any sharp edges), your piggy can go in and out and if you link them together she can run between them, stopping in each box, where you could hide bits of food as a surprise or a handful of hay for her to nibble / snuggle in. Your piggy will also get great enjoyment from chewing the boxes, try and use plain brown ones if you can (just to be on the safe side).

The Wheekies also love playing in brown paper grocery bags, they go in one end, sometimes all of them together, squashed in, and eventually nibble their way out the other end.

Source: Diddly