Poster advertising the Thames Tunnel, London, mid-late 19th century.

UNITED KINGDOM - APRIL 03: 'Open to the public every day (Sundays excepted) from Seven in the Morning, until Eight in the Evening'. Sir Marc Isambard Brunel (1769-1849), engineer and inventor, was at the forefront of civil engineering during the Industrial Revolution. His most remarkable undertaking was the Thames Tunnel from Rotherhithe to Wapping. Construction began in 1825, but was not completed until 1843, partly due to the workings being totally flooded in 1828, causing the project to be abandoned for several years. 50,000 people walked through the tunnel on the day it opened. Today it is part of the London Underground. (Photo by SSPL/Getty Images)