Ultra-high-definition cinematic artwork featuring a gargantuan Cthulhu emerging from a tempestuous sea, positioned near an ancient lighthouse perched on a moss-covered rock. The scene captures the awe-inspiring scale of the creature, evoking intense feelings of megalophobia. The setting is illuminated by atmospheric lighting and lumen reflections, creating a moody, dark ambiance with an organic luminescence emanating from Cthulhu's form. This digital painting, rendered in sharp focus with photorealistic qualities, utilizes advanced techniques such as subsurface scattering to achieve a hyperrealistic effect. The composition is meticulously detailed, akin to a photograph captured with a high-definition DSLR camera, leveraging Unreal Engine 5 and Octane Render for an 8k finish. The overall artistic vision combines cinematic movie-quality aesthetics with the fantastical elements of Cthulhu mythology, resulting in an immersive, visually stunning masterpiece.