I've walked around locks, taken boat trips through them, but recently the Canal & River Trust gave the opportunity to walk along the bottom of one. Happily, it was empty of water at the time!
The lock had been drained for repairs: about every 25 years, the large oak gates need to be replaced. Here, the top gates were to be taken out and renewed, while the bottom set were having some repairs. Planks of wood slotted into the lock walls held back the water temporarily. While the lock was dry, visitors got the opportunity to see some usually-submerged Victorian brickwork.
Near Angel, City Road Lock is part of the Regent's Canal which runs between Paddington and Limehouse, via Camden Town and Islington. Designed to link Paddington Basin (terminus of the Grand Junction Canal to the Midlands) with the Thames, it was also tied in to the development of Regent's Park by one of its directors, John Nash. The architect's assistant James Morgan was the canal's engineer.
The first stretch, to Camden Town, was completed in 1812 but among the problems delaying this second section from Camden to Limehouse was the embezzlement of funds by promoter and superintendant Thomas Homer. Caught in 1815, he was sentenced to seven years' transportation. Despite the setbacks, the canal opened in 1820, and nearby City Road Basin became a popular unloading point because it proved more convenient than Paddington Basin. It thrived in the nineteenth century, with cargoes of coal and building materials being unloaded here - although there were several proposals to turn it into a railway - but declined in the last century. Commercial use of the canal ended in the 1960s. Today, the boats which use it mostly do so for pleasure.
Want to see more of the lock? Londonist also visited, and made a video; or you could become a volunteer!