Design a visually striking fantasy book cover featuring a hidden elven city nestled deep within an ancient forest. The city is built into the colossal trees, with winding bridges and shimmering waterfalls cascading through the branches. Elven archers, clad in green and brown, stand guard on the platforms, their bows drawn. The entire scene is bathed in the soft, warm glow of dappled sunlight filtering through the leaves. The color palette is vibrant and saturated, with greens, golds, and blues dominating the composition. The camera is positioned low, looking up at the city, emphasizing its scale and majesty. Rendered as a photorealistic 3D model, with meticulous attention to detail. Masterpiece, 4k resolution.