Should I make a C&C cage for my guinea pigs?

What are somethings I can add to my guinea pigs' cage to make it more fun for them?

• Here's what their cage looks like now: http://i52.tinypic.com/2mi2rur.jpg I feel like I don't have enough things for them to do in there. Any ideas?

• Answer:

  DON'T add a running wheel. they aren't supposed to have running wheels or the balls you put hamsters in because it is horrible for their backs. My guinea pigs like brown paper bags. they can eat it, and they like to hid inside. I also use toilet paper rolls and stick snacks inside. Mine have a stuffed animal and little balls (ping pong size) to push around. I also have a small block of wood like it's 1 inch thick and like 8 inch wide idk how long, but long enough for them to lay on and they like to chew on it too. I also found these wooden toys they push around and pick up and chew on. One also loves to lay in a pile of hay... Also, just commenting on the pic. I like that yours can use a litter box. wish mine would, I have tried but it didn't work well.