One Angel Lane, formerly known as Watermark Place, replaces the redundant international telephone exchange, Mondial House, on a site that fronts the river next to Cannon Street station. The site has an important place in the history of the Thames and is defined by the boundaries of the working river. The northern edge is the line of the Roman wharf, and the 'Steelyard' under Cannon Street station was a German Hanseatic trading post, the largest medieval trading post in Britain. The strategic viewing corridor to St. Paul's Cathedral informs the height and massing of the new building.
Twin rectangular blocks to the north are attached by a full-height atrium, and the fluid forms of the lower pavilions enclose a south-facing open square with a restaurant to encourage active use. This, together with the pedestrianisation and widening of Angel Lane to the east of the site, more than doubles the existing public space and creates the largest riverside square in the City of London. The new building and its setting form a strategic part of the City Corporation's initiative to encourage access to the river and develop a unified river walkway. In order to enjoy the magnificent views along the river from Tower Bridge to Westminster, the building is clad in high-performance glazing, using dot-matrix glass with a palette of colours derived from a pixilated image of the water to create a dappled façade.