BBC News published recently a story about the Thames Tunnel, once thought to be the eighth Wonder of the World, because it was the first tunnel under a river. The only time I was in a tunnel under a river it was in 2003, in Budapest, Hungary, when I had to go down to level 2 metro line that went right under the Danube.
Once I found out that we were going straight under the Danube I was surprised. It was a chilling feeling to know that above me ships and a lot of dirt were minding their own business. Thames Tunnel was, for a long time, a great place for businessmen until the London authorities decided to put the metro in it. Still, an great engineering feat alongside the Channel Tunnel.