A public space that is easily accessible and navigable is one that provides the user an organized, seamless and enjoyable experience. The space is designed keeping in mind the user experience, understanding every user touch-point and more importantly the circulation of the space. This involves multiple disciplines coming together - architecture, interior design, product design, human psychology, human ergonomics, communication design, graphic design, etc.
The experience of a public space can be further enhanced when the user has no need to enquire and there is no chance of him being confused. The journey through the space should be effortless as he navigates exactly how he is supposed to without asking for instructions. He has the choice to go "left or right" only when we need to give him a choice. This is exactly where effective communication design comes into play. Way-finding, signage systems, environment graphics and other communication design elements not only make the journey easier but also enhance the experience. It allows the space to "talk" and communicate with its user and in many ways direct the experience.
Effective use of communication design in space can ensure the user is doing exactly what you want him to do and how you want him to do it. Not-so-effective communication can make the journey confusing and maybe even chaotic.
An instance of visiting the Apartheid Museum in South Africa is a relevant example here. When you enter the museum, you are randomly told to enter from one of the two entry points - Whites or Non-whites. It was brilliant. The true understanding of what South Africa went through during Apartheid begins even before you see any exhibit. I can never forget that journey. On the other hand there are so many other public spaces that I have not enjoyed and had difficulty finding my way through, simply because of lack of communication or poor signages. Railway and Metro networks in some parts of the world are usually difficult to steer your way through. Airports and malls as well are places where you need to ask almost ten people to find the washroom or the escalator! A sound signage and environment branding system will make any place more successful.