There is no inside, no outside on this surface. Some people have suggested that the Universe is a similar object, but in 4 rather than 3 dimensions. That is, a finite 3-dim geometric hyper-surface (in a 4-dim space) with no boundary, no inside / no outside.

If you think there's an inside, imagine yourself walking straight on the side that you think is pointing towards the "interior", and you'll soon find yourself "outside".