The ongoing decay of urban stone structures creates a need for smart materials that enhance durability over the life cycle. Biotechnologies based on fungus Pleurotus ostreatus are explored as a method to strengthen substrates prone to destruction in this study. Their ability to alter properties and adapt to extreme conditions provides the basis for self-healing, strong, resilient, and environmentally friendly biocomposites. Some fungal strains are known to precipitate calcium carbonate (CaCO3) and to heal cracks in concrete, while Pleurotus ostreatus stimulates calcium oxalate (CaOx) formation. The study investigates whether these microorganisms are able to facilitate carbonate biomineralization without compromising their ability to act as natural sealants. The resulting Mycokarst material, formed from CaCO3-based karst soil, rice, dolomite flour, and Pleurotus ostreatus mycelium, demonstrated cyclic self‑healing and strength gain. It promotes self-strengthening of weak karst soils and stone structures through the formation of mycelial and limestone frameworks without external intervention. Mycokarst represents a new generation of smart biocomposites and offers a green approach to protecting urban mineral-based infrastructure from decay, while reducing CO2 emissions and environmental impact and minimizing human and technological interference with construction and restoration.