A blue plaque has been unveiled 40 metres underground on a wall in HS2’s Euston tunnel between Old Oak Common and Euston, which marks the last resting place of Sir Marc Brunel and his son Isambard Brunel. HS2 Euston Tunnel under construction. In 1825, it was used to excavate the world’s first underwater tunnel underneath the River Thames in London. HS2 CEO Mark Wild and Katherine McAlpine, Director of the Brunel Museum, at the Brunel plaque unveiling in the Euston Tunnel. Such monitoring took place underneath Kensal Green Cemetery to ensure construction took place safely, conscientiously and with respect.