You probably think of Isambard Kingdom Brunel in the context of the Great Western Railway, the SS Great Britain or the Clifton Suspension Bridge. However, he started his engineering career helping his father build a tunnel under the Thames, and nearly drowned in the process.

Marc Brunel was born in France and after avoiding revolutions in France and America he ended up in England. His first major claim to fame was designing a machine to create the wooden blocks used in the rigging of sailing ships - over 130,000 were needed each year and up to 1802 they were all carved by hand!

Various people had considered building a tunnel under the Thames to allow goods and people to cross down stream of London Bridge without having to pay the ferryman. The early attempts ended in failure and a declaration that it was not possible. Marc thought a solution could be found and designed a tunnelling shield to allow 36 miners to "safely" dig out the clay ahead of the shield before it was moved forwards.

Our tour started in the Rotherhithe caisson - a brick ring which slowly sank into the ground to form a large, cylindrical shaft. Once at the right depth then the middle was excavated and Marc was happy that the bottom aligned with a suitable bed of clay which extended under the river.

Initial progress on the 3 year build was good but then various disasters struck including financial challenges, illness, flooding and unexpected ground conditions. It was 18 years before the tunnel was finished and then only as a foot tunnel - the original plan had been to have ramps to allow horses and carts to use the tunnel.

Isambard joined his father very early on and worked up to 36 hour shifts supervising the works. On one occasion he was in the workings when the Thames water flooded in and he was washed down the tunnel and up inside the shaft where he was rescued. Having broken some ribs and ingested quite a bit of Thames water (which was London's main sewer), he was not too well for a while!

We enjoyed an interesting talk about the history of the tunnel, the catastrophes and the successes as we sat about halfway down the shaft. Below us the trains of the Windrush Line rattled through the tunnel.