Forgotten spaces, often referred to as lost spaces or non-places, represent a crucial challenge in contemporary urbanism and sustainable urban development. They are underdeveloped and undesirable urban areas that are in urgent need of rethinking, replanning, and redesign. They are mostly undefined, lacking measurable boundaries and communication routes. These natural areas are usually neglected and underutilized, which leads to their insufficient exploration from an urban-ecology perspective. Due to the impacts of climate change, it is necessary to reintegrate these lost places into urban planning. In organized non-spaces, it is crucial to rediscover their function and make these areas accessible or released for use. Wetlands, rich in biodiversity in urban areas and subject to seasonal changes, are threatened by human activity, and their protection is essential for the sustainable development of cities and urbanism today. Cities are interwoven with such non-places, which exhibit various characteristics within the urbans system. In conclusion, unrecognized urban spaces and lost wetlands represent an untapped potential for sustainable urban ecosystem development. This shifts the perception of urban voids from traditional urbanization towards their new potential as spaces for green development within the framework of sustainable contemporary cities.

Urban green spaces of collective housing are more than a passive background: they are living records of how cities have understood the relationship between housing, nature, and society. In many parts of Central and Eastern Europe, particularly within housing estates built in the late 20th century, these green spaces were carefully planned as part of a larger ideological, spatial, and social framework. Today, however, their original functions are often obscured by decades of political change, privatization or shifting management practices. This paper explores six residential areas in Nitra, Slovakia, analyzing how their design, amenities, and open spaces reflect wider societal transformations. Special attention is given to urban green spaces and urban voids—often overlooked yet critical elements of the everyday urban experience. Using a multicriteria method, we evaluate and compare these developments considering both historical and contemporary urban challenges, including climate resilience and sustainable regeneration. Our approach combines archival research with on-site fieldwork, spatial mapping, and qualitative observation to explore how the planning of collective housing has changed and what it means for the future of urban living. The results reveal a gradual decline in the quality and function of open space in collective housing, especially in newer projects where ecological and social values are often neglected.

Competences in the construction sector of the Slovak Republic (SR) under the current legislation are exercised at the local level of the state both by institutions of local self-government (municipalities) and state administration (district offices). The building authorities with the authority to decide on building permits are currently the municipalities to which the state has delegated building competences by Act No. 50/1976 Coll. on spatial planning and building regulations, as amended. However, the new construction legislation, effective from 1.4.2024, leads to a retroactive transfer of construction competences from municipalities to the state, to the newly created regional construction authorities. The long-awaited change in the legislation in the field of building regulations is expected to shorten the permitting processes and improve the functioning of building authorities. Municipalities will carry out the spatial planning, but the issuance of decisions on construction will be the responsibility of the state. The research presented in the paper, conducted through guided interviews with municipalities and district authorities in two selected regions of the SR, demonstrated the lack of state preparedness for the operation of the new state policy in the construction sector. We have come to a similar conclusion by theoretical analysis of the opinions of domestic and foreign authors. Optimal functioning of cooperation between state and local authorities would be possible with future legislative adjustments to the redistribution of construction proceedings between state and local self-government.

Urban emptiness is a recurring spatial condition across contemporary cities, resulting from long-term planning decisions, functional transformations, and shifting socio-economic dynamics. Urban voids are often interpreted as signs of failure or neglect; however, they also represent flexible and open-ended spaces embedded within everyday urban environments. This study develops and tests the Adaptive Void Assessment Framework (AVAF), a five-dimensional typological instrument applied to n = 33 urban voids identified through a systematic grid-based field survey (100 × 100 m resolution) in the central urban zone of Nitra, Slovakia (March 2025–January 2026). The framework evaluates sites across nine indicators spanning openness, social appropriation, ecological succession, temporal persistence, and institutional flexibility, yielding composite Adaptivity Index scores and four dominant adaptive regimes. The findings demonstrate that 34% of identified voids function in a socially active regime while 14% exhibit ecological dominance, with a moderate positive correlation identified between temporal persistence and adaptive capacity (r = 0.46, p < 0.05). This challenges conventional deficit-based classifications and reframes urban voids as active components of the urban metabolism capable of enhancing ecological connectivity and spatial flexibility within post-industrial urban landscapes. This reframes urban voids from residual outcomes of urbanization to spaces with potential for green integration within sustainable contemporary cities.