To get an idea of what it's like inside an underwater submersible, we come to an industrial estate in the Dutch town of Breda.
This is the home of U-Boat Worx, which makes a range of submersibles.
Most of them are bought by private yacht owners to use for their own projects, but plenty are used for research and exploration.
None of them go as deep as the wreckage of the Titanic; they're not designed for those depths.
But in front of us is the Cruise Sub-7, a seven-person submersible that's got roughly the same dimensions as the missing Titan vessel.
One difference is immediately obvious.
At the front and back of this machine is a large acrylic window that allows a wide view of the outside world.
The Titan is different, with a very limited view through a single porthole.
I climb a flight of steps to reach the top of the submersible, then go down four steps of a ladder into the sub itself.
Three things strike you straightaway - the light that comes in through the windows; the sophisticated instrument panel and the small size.
The light will have gone even by the time you get to a depth of 300m - it's dark at that depth.
But the sub has powerful exterior lights and that would ease the sense of claustrophobia. On the Titan, you don't have that - it must feel much more as if you are trapped in a box.
The instrument panel is another key difference - the Titan, as everyone now knows, is partly manipulated by an old Playstation controller, and does not have international safety certification.
The Sub-7 is fully certified, and has an array of controls for normal manoeuvres, emergency response and communications with the surface. All of that provides reassurance.
The list of "failsafe guarantees" in case of problems is long.
But then there's the size.
You’d only expect to stay on the Sub-7 for an hour or two - eight hours at the most - and I don't think you'd want to stay longer. With seven people inside, it would feel cramped.
There is certainly not enough space to stand up straight and moving around is difficult. The prospect of being trapped inside a submersible of this size for days on end would be utterly grim.
By Adam Parsons, Sky News Europe correspondent