Envision a breathtaking underground cathedral, its vaulted ceilings adorned with shimmering crystals that reflect ethereal light in a spectrum of colors. The walls are lined with intricate rock formations, creating a natural yet mystical ambiance. Lush greenery and bioluminescent plants weave through the space, while a tranquil stream flows gently, casting rippling reflections on the crystalline surfaces, inviting serenity and contemplation in this hidden treasure.