Limit-Space is an architectural speculation. It constitutes a spatial logic resonating with the ontological subjectlessness embraced by the 21st century and its myriad of multi-specie agencies, human and non-human, organic and non-organic, natural and artificial. Conceived, built and inhabited by a myriad of xenos emancipated from the absolute subject of modernity and the relational subject of postmodernity, Limit-Space is driven by a primary vocation: that of defying both the Promethean flatness of the Platonic chora and the baroque fluctuations of the Aristotelian topos by fiercely opposing their 20th century common architectural condition: that of being measurable, that of being sistematizable, that of being homogeneous, that of being modern. Liminal in its mismatched interplay of pressures, limited in its massive figurative determination, and limitrophe in its foliated consistency, Limit-Space capitalizes on the Roman territorial notion of limes. Its spatial nature as differential sameness and auto-referential difference particularly impacts on the conception of the floor as an architectural element: it reformulates its continuous and discrete attributes by formal and performative differentiation, recovering some of the morphological traces characteristic of pre-modern architecture while marking a definitive departure from the architectural gestures associated with the 20th century. The book proposes a spatial logic both opposing the spatial configurations characteristic of the 20th century and establishing a dialogue with the current death of the notion of subject. It narrows down the discussion through three triangular associations in between Space, Subject and Floor, historically contextualizing the first two and speculatively developing the third one, considered to be surreptitiously blossoming in the current state of art of experimental architecture.