Futurama
episode I, Roommate

To visualize a finite universe in three dimensions, you can watch the Futurama episode I, Roommate (Season 1 DVD): [Fry and Bender are looking for housing. Leela, Fry, Bender and the manager enter into an apartment that resembles Escher's "Relativity". Fry says that he is not sure that they want to pay for a dimension they are not going to use. Then Bender, the robot, falls down the staircase and continues to fall "down" the other staircases in many different directions.