A hidden residential city located deep within a massive crystal cave, where entire neighborhoods are carved from natural quartz formations. The crystalline walls reflect light in rainbow hues, creating an ethereal glow throughout the underground community. Homes are built into the cave’s walls and floors, using transparent materials that let natural light filter in from skylights above ground. Waterfalls flow through the cave, feeding into tranquil underground lakes that serve as communal areas for residents to swim and relax. The entire city is a hidden gem, blending nature’s wonders with futuristic living.