The continuing growth of urban populations has intensified the need for cities to provide conditions for a healthy and creative way of life, work, and leisure activities. From the aspect of spatial planning in cities, the key is to have a public space network of sufficient scope and quality. “In addition to public space, which is public in terms of ownership and use, private space open to the public is important” [1], i.e. space that is “privately owned, but in public use. It comprises parts of private structures and their external areas” [1], such as green areas, squares, atria, shopping centre arcades, movie theatres, and similar. The development of network of private space open to the public in Slovenian cities was not planned, but was driven by owners’ profit motivations. The study findings presented in this paper show that private space open to the public could complement and improve the city’s public space network to a greater extent than now, and that this should be pursued in a planned manner. “By analogy with Slovenian mountain trails that already constitute an extensive network” [1] of private space open to the public outside towns and cities, we suggest the planned development of the network of private space open to the public in urban areas as well. It is connected with, and complementary to, public space. The enforcement of this special spatial planning category can be achieved through urban planning practice, i.e. by using urban design guidelines and by working towards their gradual introduction into legislation.