In the deep ocean trenches live colonies of amazing animals beside ‘smokers’ – hydrothermal vents that belch out hot water and nutrients. In principle I would love to see the giant clams, and white two-metre-long tube worms with waving red plumes, but there is a problem. Fear.

Two miles down, the water pressure is 300 times atmospheric pressure – enough to squash you flat if you were exposed to it. I have met two brave women scientists who have been down there, in a tiny sphere made of titanium, which is exceedingly strong, but I tremble at the thought of that much pressure. In the Science Shack series last year I occupied an ‘aquashack’ made from a couple of rubbish skips, one upside down and welded to the other. This elegant residence was dumped on the bottom of a pool three metres deep, which was plenty deep enough for me.

The series Building the Ultimate (Tuesdays at 9 on BBC2) includes helicopters, suspension bridges, and spacecraft, but it kicks off with submarines, the dare-devils of the deep.

The first ever submarine was made in London by Cornelius Drebbel, around 1620. He showed it off to King James I, who wisely declined a ride inside. The craft was essentially two rowing boats, one turned upside-down and sealed on top of the other, like a wooden version of my aquashack. Allegedly they rowed it from Westminster to Greenwich and back under water in three hours, which I find hard to believe.

A propeller-driven sub was built during the American Civil War, and in 1879 an Irish rogue called George William Garrett built a steam-powered submarine, and launched her from Birkenhead. Unfortunately she ran into bad weather and sank, near Rhyl in North Wales. She was called Resurgam, which is Latin for ‘I will come up again’, but she never did. Indeed she still lies ten fathoms down off the Welsh coast.

I do not believe I should enjoy the claustrophobia of a submarine, nor the idea of springing a leak. And experienced submariners tell me that the lavatories, which use a suction system like those on aircraft, can go wrong when they are put under positive pressure to offload the accumulated sewage; if someone is rash enough to use the heads at the wrong moment, the entire sub fills instantly with malodorous brown fog.