Today marks the 50th anniversary of an exploration that is probably equivalent in scope to the first moon landing but has received much less attention.
On Jan 23, 1960, Jacques Piccard (son of Auguste Piccard who was the real life inspiration for Tintin's Professor Calculus / Tournesol) and US Navy Lieutenant Don Walsh reached the bottom of the Challenger Deep in the Mariana Trench, some 10.9 km below sea level with the Bathyscaphe Trieste designed by Auguste Piccard.
Down there, the hydrostatic pressure is roughly 1100 bar, and as somebody who has used this kind of pressure in the laboratory, I can state very firmly that I wouldn't want to be there, not for all the fame and glory in the world. It's bad enough keeping 1100 bars inside your equipment when you're on the outside, but the reverse situation doesn't bear thinking about.
Understandably, nobody has come forward to repeat and expand on this exploration, so the deep sea is still a territory about which we know next to nothing. We do know that there is life down there, but biological excursions with submarines such as Alvin have typically been limited to a range of around 4,000 metres.