Architecture is experienced through numerous physical and psychological factors. Generally, a person's fundamental understanding of an architectural work comes from the way they engage with its spaces. A journey through Carleton University's second, forgotten tunnel system is an experience that provoked intense reactions through multi-sensory perceptions - reactions comparable to the cinematic and literary genre, horror. By drawing parallels with this narrative medium, this thesis follows a path with choreographed movements through space; a journeying into the tunnels. Understanding what makes some spaces horrific, and therefore the occupant, horrified becomes an essential exercise that offers insight into how people perceive space. While discomfort is not typically part of the architect's repertoire, Behind a Door that Doesn't Exist sets out as an exploration into the psychological effects of architecture's limits of the mind and body. We enter an architecture considered too dangerous, even horrific, for the occupants it was built for.