Aquatico

"Aquatico is a single-player, open-world city-builder game set on the ocean floor, where players must build a unique underwater city to escape a dying world. The game features excellent gameplay, splendid visuals, and beautiful music, as well as the challenges of managing resources, temperature, and depth to survive in the diverse biomes of the sea. Construct core infrastructure on the seabed and house your people in the safety of domed layers above, but be wary of the dangers that lurk in the depths."