What steps should people take to build an "underwater city"?

In the near future, people will also build an "underwater city", which is no longer a fantasy, but is approaching reality step by step.

Step 1: At present, Japan is building a "small city" for swimming at sea. Its main body is made of steel, and its center is a six-story building. There is a small indoor garden, a cinema, and all the water and electricity are self-provided. This swimming city is supported by eight tall columns. Put them away and you can sail like a boat.

A large number of fishery resources on the seabed

Step 2: There is a "sea park" in Longchuan Bay in the southwest of Shikoku Island. People can enjoy the wonders of the sea through the 60 cm diameter 16 glass window.

Step 3: Since the first underwater laboratory was built in the United States, many countries have followed suit and built "steel houses" and other buildings on the seabed. The air pressure in the "house" is the same as the sea surface. People can work normally, repair oil and gas wells on the seabed, salvage sunken ships, explore the seabed and so on.

/kloc-within 0/00 year: the population on the ground is increasing, and the housing is getting more and more tight. What shall we do? Only go to the ocean. It is said that a group of Japanese engineers and architects have planned to build the world's first "marine city" in the sea area 20 km away from Tokyo/Kloc-0, so as to solve the human habitation problem in the future.