I've been there. It's very f*** cool. It's sort of like the old underground metro subway stations in Sydney australia. You know the old circular key line with Martin place museum Hyde Park these type of stations on them? I can't remember all the names now but they have that old tiling and the long pedestrian tunnels and I mean just a fantastic kind of vibe to go into them and this tunnel is like that but it goes under the water.

I think there might be a similar tunnel in Antwerp, Belgium (great city, awesome Jewish bakeries) I seem to recall having transited such a place in that region too.