A photorealistic depiction of a hidden residential city deep within a colossal crystal cave, where neighborhoods are sculpted from natural quartz formations. The crystalline walls refract light into dazzling rainbow hues, casting an ethereal glow across the entire underground landscape. Transparent, modern homes are seamlessly integrated into the cave's walls and floors, allowing sunlight to filter in through meticulously placed skylights above ground. Cascading waterfalls weave through the city, feeding into tranquil underground lakes that serve as serene communal spaces for residents. The design merges futuristic living with the natural splendor of the cave, illuminated by soft ambient lighting and shimmering crystal reflections. Ultra-high-definition rendering with intricate details, realistic textures, and dynamic light play, creating an awe-inspiring visual experience.