As in can someone dive to the euro tunnel like swim above it? I haven’t ever seen pictures of the tunnel actuallf under the sea!
Also how does it not implode like the submarine?
The tunnel in under the seabed. Hence (a) you can't swim to it and (b) it isn't being crushed by the weight of water above it, as that water is being supported by the rock through which the tunnel was drilled.
It’s 40 metres under the sea bed, so no. Its route will be known so with a bit of expert assistance and if you’re a top swimmer you could follow the route over the sea. Great engineering feat!