One of the world's earliest underground tube railways opened in the Tower Subway (interior depicted), a tunnel beneath the River Thames in London.

The Tower Subway is a tunnel beneath the River Thames in central London, between Tower Hill on the north bank of the river and Vine Lane on the south. In 1869 a 1,340-foot-long (410 m) circular tunnel was dug through the London clay using a cast iron circular shield independently invented and built by James Henry Greathead, similar to an idea that had been patented in 1864 by Peter W. Barlow but never built.

The River Thames, known alternatively in parts as the River Isis, is a river that flows through southern England including London. At 215 miles (346 km), it is the longest river entirely in England and the second-longest in the United Kingdom, after the River Severn.