a hidden underground city with bioluminescent plants lighting the way

underground city subterranean civilization bioluminescent plants hidden community secret society architecture illuminated tunnels urban spelunking eco-friendly living infrastructure flora cavernous habitat culture mysterious settlement eco-urbanism design pathways enclave green technology sustainable subterranea landscaping exploration cave dwelling concealed metropolis ecosystem cityscape secretive sanctuary world marvel wonders biodiversity gardens eco-urban planning discovery subcity utopia subculture dwelling community