The recent mechanisation of architecture and movement has reduced the degree of environmental diversity in architecture and the urban realm. Biological sciences suggest that diversity, within a certain range of variation, is desirable to exercise the adaptive capacities of any living organism; a slight instability being the necessary condition to true stability. Environmental diversity can be achieved within the variables of architecture by subtle articulations between interior and exterior environments. Such diversity is examplified by parametric simulations of the environmental behaviour of some transitional spaces generated by the interpenetration of massive and transparent structural elements. Transitional spaces favour environmental diversity and a progressive physiological adaptation to avoid discomfort generated by abrupt environmental transients. At the scale of the city, the public and semi-public realms are seen as generators of such diversity. The extent of the transformation of city centre and the underlying isotropisation is illustrated morphologically through the study of two cities. The movement of the contemporary urbanite is found to be much more restrained than that of his ancestors living in traditional urban fabrics. A theoretical investigation of environmental transients through the manipulation of a thermal comfort equation highlights the possible extent of such transients according to combination of wind and sun exposures. Practically, a survey method is introduced to measure the extent of environmental transients as experienced dynamically by a pedestrian when moving through the archit€cture of the city. An extensive survey campaign of existing arcades allows for the discussion of their environmental performance according to certain property-ratios. The arcade type, which preceded the mechanisation of architecture and movement, stands as a clear example of the ability of architecture to generate environmental diversity through urban continuity within its own variables. Such transitional spaces provide a moderate stimulation of the senses through a progressive physiological adaptation and therefore favour optimal receptivity of the moving being to its built and social environments.