International Space Station has reached its end of life and new space stations are planned. I would like to propose an International Underwater Station which would benefit humanity more than its space counterpart. An underwater habitat was described in Jules Verne's "Vingt Mille Lieues sous Les Mers" almost two centuries ago. However, we are still leagues behind creating such habitat even though we have the technology. We should start by creating an underwater research station. It would be made of specially designed submarines. These submarines would be cascaded like the space stations sections are attached to one another. As time goes by more sections would be added and the old ones would be removed.
International Underwater Station would make research on deep-sea habitat and would also clean the surrounding region as it explores. It would create underwater farms to feed its occupants like in Jules Verne's novel. With a nuclear reactor on board, it would be a self-sufficient habitat.
An autonomous ship above water would accommodate the submarine to assist in logistics and as a rescue boat in case of emergency. A smaller version of this underwater station would be deployed on Mediterranean Sea first, then a larger version on the oceans.