This is an animation depicting a type of large-scale space colony called an O'Neill Cylinder, made popular by American Physicist Gerard K. O'Neill in his book The High Frontier: Human Colonies in Space (1976). Two cylinder are needed to act as a gyroscope to prevent the system from precessing. The cylinders here measure 9.2km (5.6 miles) in diameter and 36km (20 miles) long. Rotation about the long axis, at a rate of 210 m/s at the surface (2.3 minutes per rotation), provides artificial 1g of artificial gravity by means of centripetal force. The video shows the structure from space, then we enter the interior and fly along the central axis.