Humanity has built cities in deserts, mountains, forests and on islands, but why do we still only live on the surface of Earth? More than 70% of our planet is covered by water, yet almost all of humanity lives on land.

What if the next step for civilization isn't moving to Mars but moving underwater? Imagine giant underwater cities powered by nuclear energy or ocean currents, connected by transparent tunnels and protected from storms, heatwaves and rising sea levels. We could create entirely new living spaces without taking up more land on the surface.

Of course there would be massive challenges like pressure, construction costs, oxygen production and maintenance, but every great civilization project sounded impossible at some point.
The real question is: if humanity had the technology and the money, would living underwater be more realistic than colonizing another planet?