Why does my guinea pig sit on top of his igloo (house)???? ?

it just started a few days ago. every time i check on him he is either eating, drinking, or on top of his house thing. i kno he can fit in it, i watch him sleep in it b4 i go to sleep also. i dont understand. i got him a friend but they fought and i kno why tht happened. i just dont understand why he is always on his house. can anyone help?