Dear Evil Engineer,

I am a reclusive billionaire, seeking peace in retirement after a long and tyrannical career. Being even more misanthropic than the typical villain, I would like to live as far from human civilisation as possible: the bottom of the ocean.

Could you advise me how to build a lair on the ocean floor?

Yours,

An aquatic villain

Dear villain,

The bottom of the ocean is a prime piece of real estate for a villain who values solitude and aesthetic considerations: there is nothing quite like a goblin shark or a giant isopod floating past your toilet window to reassure you that you have (at last) found Hell on Earth. I’m pleased to say that an underwater lair is possible, from an engineering perspective, and – as a billionaire – you may even have the means to make it a reality.

We have come quite some way from the age of the diving bell. Derring-do French oceanographer Jacques-Yves Cousteau led the first ‘Conshelf’ project in 1962, which supported...