Wild guinea pig species (like Brazilian guinea pigs) make their homes on grassy plains, where there is ample grass and other vegetation for them to feast on. They are herd animals, with groups usually consisting of a few females (called sows), a male (called a boar) and their young. This need for socialising means that they are most comfortable with members of their own species, and so owners of the domesticated species often keep them in pairs or threes.
Guinea pigs love socialising with each other
Unlike other rodents, guinea pigs don’t make their own burrows, preferring to hide from aerial predators under vegetation and within grass tunnels. Guinea pigs that are kept as pets today retain some of this fear of wide open spaces, so it's a good idea to offer them a small enclosed space into which they can run if they feel a little uneasy. Examples of this are hideaways and tunnels that you can put into your pets' run.