This design speculates on the concept of interiority: embracing its qualities as necessary and imminent components of urbanity, as cities increasingly densify. The project proposes a fitness centre, hotel, and sports club for the South China Athletic Association in Hong Kong’s densely populated Causeway Bay area. Boundaries of the interior and exterior are reinterpreted to simulate fitness and recreation. A series of highly pressurized apertures are oriented horizontally and vertically to act individually as centripetal involutions. They penetrate an otherwise solid mass to mediate media such as light, air, color and horticulture or recreational activities like running or hiking. Interiorizing these media gives each a sense of artificiality. The combined network of involutions displaces the natural into preternatural situations. The strategy of pulling the outside in and pushing the inside out deforms recreation and urbanity into a productively unstable state of interplay, and an exploration of urbanity landscape and architecture.