Underwater habitats are structures designed for humans to live and work beneath the ocean's surface. These habitats provide a controlled environment where researchers can study marine life, conduct experiments, and explore underwater ecosystems. They are often equipped with life-support systems, allowing for extended stays underwater. These habitats can vary in size and complexity, ranging from small research stations to larger facilities like Aquarius Reef Base. They are typically anchored to the ocean floor and connected to the surface by a series of airlocks and tunnels, ensuring safety and accessibility for inhabitants.