A colossal oceanic trench megacity built into a massive underwater canyon formation, towering bioluminescent crystal spires reaching toward the surface far above with internal cyan glow, suspended glass biodome districts floating above hydrothermal vent fields, sleek hydrodynamic submarine craft navigating between glowing windows, massive atmospheric exchange towers harvesting oxygen from upper water layers, deep navy and phosphorescent teal palette with soft ambient light filtering through ocean depths, epic upward shot from deep plaza with tiny silhouetted divers on observation platforms emphasizes impossible underwater engineering scale, photorealistic, cinematic depth of field