Guinea Pigs like all living animals need plenty of exercise. When you let them run around on the floor you will see how much they really enjoy a good run. When they are happy and feel safe they "Pop Corn" while running or standing still. It's quite cute to see a piggy all of a sudden start randomly leaping in the air. When I first saw this Kornage was on the sofa with me, running up and down. Then all of a sudden he started doing it, at first I thought he was having a convulsion. I now know this to be pop corning. When your piggie's are in a group, if one starts to do it you will notice most of the time the others will too. It's really very cute to watch. Kornage pop corns the most when he is on the floor with the girls. We have nick named him Bucking Bull because that's what we liken it too.
If you let your Guinea Pigs run around freely in doors you MUST make sure you block off all cables. Millie Nawty Moozer has chomped her way through lots of my cables. A long story so I will keep it short, even when you block off all places your Piggie's can get to that have wires there, your friends unblock them unknowing to you by accident! I had to replace 3 network cables, one scanner cable, speaker cable and the sky cable! you get my point here ?
If you do put your Guinea Pig on the floor and they have had newspaper in their cage, try putting some down on the floor. I found my piggie's liked to use this to go to the loo on.
You can also get small animal litter trays. They are not like cat litter trays, they are made in a triangle shape with one corner higher. Some Guinea Pigs like to back up in to something when they go to loo but this is not the case with all, as only Nutmeg shows this behaviour.
I keep my Cavies in the living room and they run on the floor, I have found they actually go back in to their cage to pee. They will leave pellets on the floor sometimes though but they definitely like to use the cage to urinate. This is something they started to do after a while with me. I think they are now used to their surroundings and know where to find their cage.
I have read online that Guinea Pigs do not climb or jump. This is true to 3 of my pigs but Millie can jump up four courses of brickwork. I have a small wall in my garden and she can easily get on top of it. She also uses things to climb up on to. So just be careful when you let your Guinea Pigs get exercise.
I have found when the Guinea Pigs are in the run on the grass they do not run around as much as they do when I have them on the patio.
They get their most exercise in doors on carpet. Out of options this seems to be their most favourite.