Underground Valley City: A Cartoon Cavern Dream

In a vast underground cavern, a lush valley unfolds with a meandering silver river, soft pastel hills of stone, and glowing fungi along the banks. A whimsical underground city is built into the cavern walls and towering stalagmites, with rounded stone houses stacked on terraces, colorful balconies, rope bridges, and cobbled streets. Lanterns glow warm orange, pink, and teal, casting bold shadows in a cartoon world with thick black outlines and flat shading. Characters wander along market stalls and stairways carved into rock; friendly creatures peddle trinkets as miners-turned-artisans pass by. The ceiling is dotted with stalactites; distant tunnel entrances hint at more caverns. The overall mood is cheerful, adventurous, and cozy, rendered in a bright, simplified cartoon style.