Many have dreamed of a serene life floating upon the ocean, yet that dream is not completely realistic. Hurricanes, tidal waves or tsunamis, and even normal weather all affect the surface of the sea. Waves in even the mildest weather can crest far above any reasonable height, and the troughs can be devastatingly low. For those who wish to consider a watery home far away from land, living under the sea is a much better option.
Beneath the restless waves and the weather above it, the sea is generally a calm and fairly predictable place. There are many currents throughout the oceans of the world, but the majority of them have been accurately charted. Their movements during the season, their strengths, and even their temperatures are already known. Life under the sea could be a calm and restful spot for those with a preference for living in the ocean, and it could become a safe haven for thousands in need of work or homes.
Life would not be the same as living on the land, and it could easily be equated with living in the void between planets. While there is water that does contain plenty of air, the pressure increases rapidly with depth. Keeping the water out and the air in will require massive structural bracing, but it must also be flexible enough to endure the constant movement of the surrounding water.
There are not yet any cities being developed at this time for undersea dwelling, commerce or manufacturing. Some plans have been made, but no actual projects are in the works or planned to be started for at least a decade. While it is possible for cities under the sea to be built with current knowledge and materials, the world has not yet set its sights on this new and interesting habitat as a permanent home for mankind.