This graduation project aims to explore the possibilities and the pitfalls when designing a pedestrian tunnel with mirrors. The research topic was derived from an assignment given by Studio Roosegaarde, a social design lab based in Rotterdam. The major problems this project aims to solve is that a designer has no systematic guidelines to follow when designing a pedestrian tunnel with mirrors. The context this work selects is Maastunnel in Rotterdam for the reason of simplicity, accessibility and its history between Studio Roosegaarde. The keystone to the problem raised is reckoned to be the understanding of the space perception in a pedestrian tunnel and how the mirrors can alter the perceived space. A dozen of visual elements in space perception are identified through the literature survey. With the understanding to mirror perception, a handful of visual cues are selected for further step evaluation. The evaluation includes a questionnaire showing 24 photos of pedestrian tunnels to be rated. Through the survey, the correlation between the perceived visual cues and the sense of spaciousness is analysed. The visual cues correlate with the sense of spaciousness from strong to weak are the width, the height, the cleanness, the brightness of the tunnel and the reflectivity of the wall. Thanks to the lighting simulation software Dialux, several attempts of using mirrors to alter the visual cues were made readily. The exploration reveals two most promising ways of using mirrors in a pedestrian tunnel: mirrors as the Space Doubler and mirrors as the Light Splasher. These two ways of mirror usage are put to test in scale models. Regarding the Space Doubler, it is firstly found that putting mirrors on the ceiling, referred as catoptric-heightening, may significantly enlarge the perceived space, resulting in a more open and spacious tunnel. A similar but less potent effect is also found when putting mirrors on the lower part of the walls (referred as catoptric-widening) to extend the perceived width. The observers reported feelings of disturbing and dirtiness when perceiving the catoptric-widening mirrors in a pedestrian tunnel. Regarding the Light Splasher, the experiment reveals that the mirror-induced brilliance, or reflected-brilliance, can effectively increase the brightness of the space. Contastly, the complex lighting pattern created by reflection ( reflected-deflection) is not beneficial. However, it is found that the associability plays a more significant role in the perception to a space with brilliance. The observers are likely to associate the reflected-brilliance with the starry sky henceforth they perceive a higher ceiling. According to the above findings, a list of design guidelines is formulated. The design guidelines lists almost 19 dos and don’ts, corresponds to a dozen different aspects such as openness, spaciousness, aesthetics, privacy, security, etc. This project has made a self-evaluation to the design guidelines by making a design according to which. The prototype of the design has shown the strength of the guidelines meanwhile revealing the inadequacy of the current version. The guidelines are considered useful in the early stages of design process while it lacks of guides related to the size and variation of mirrors. To further develop the guidelines into a more comprehensive version, a dynamic or fully-immersive environment is suggested as the necessary future works.