In Victorian London, many miles of subways were constructed to distribute essential services including water, hydraulic power, and (later) electricity. These meant that maintenance and upgrades could be made without needing to dig up roads. Around 15 kilometres of tunnel were built - up to 3 metres underground and often associated with highway improvement works.
Dating from around 1861 onwards, many of these subways are still in use today but cannot be accessed by the public. One of the longest stretches runs under the Victoria Embankment, constructed between 1864 and 1870. Others run along Holborn Viaduct and radiate from Piccadilly Circus. The map marker is at one of the entrances to the Victoria Embankment section, beneath Boudicca’s statue.