On occasion, he is allowed to leave his box and run around on the floor. We have allowed him to do this often enough, that he wants to get out every day, and run around.
His box has a lid which we keep open a small amount to allow fresh air to circulate, in addition to the air holes in the box. For Olaf, it is a struggle, to try to get out. Sometimes, he can be found trying to jump up the walls, trying to get out. On occasion, he makes it to the top of the wall, and can be seen sitting on the fence, as it were.
He is a good little gerbil, and with a little coaxing, we are able to get him to return to his box without to much difficulty.