Waterloo International railway station

The terminal was commissioned by the British Railways Board and European Passenger Services for the trains that were to run through the Channel Tunnel. Nicholas Grimshaw's practice entered a competition run by the British Railways Board, whose brief was an extension to the existing station. The terminal replaced the old platforms 20 and 21, demolished in the early 1990s, on a narrow strip of land to the west of the station.

Largely prefabricated, the building was finished in 1993, a year early, while the Channel Tunnel was not yet ready; it opened in 1994. Its awards include the European architecture prize named after Mies van der Rohe and the RIBA President's Building of the Year.

In 2007, once the high-speed line was complete, Eurostar services moved to St Pancras and the international platforms at Waterloo closed. The terminal then stood unused for more than ten years. AECOM, with Weston Williamson + Partners, converted it to bring it into the main station, and it reopened for good in 2019.

The site is tightly constrained: an irregular strip narrowing from 55 m to 35 m wide, with the building following the curve of the tracks. Nicholas Grimshaw and the engineer Tony Hunt answered it with a repetitive yet adjustable roof structure: the curvature of the roof, fixed early in the design, led to a system of standardised struts, mass-produced but adjustable to suit their position. The roof is asymmetrical; its arches are made of two dissimilar curved trusses of triangular section, with compression members of steel tube and tension members of solid steel. The curve is steeper on the west side, where the trains passed very close to the structure.

The roof stands on a grid of cylindrical concrete columns rising from car-park level to the platforms. Its glass panels let the blue steel frame be seen from the platforms. The curved skin answers to the site and to the proportions of the Eurostar carriages; the translucent glazing opens views towards Westminster and lights the concourse all day.

Beneath the roof, a two-level viaduct carries the platforms and holds two floors of passenger spaces. The terminal brought together everything international travel required: security screening, immigration and customs. Departures and arrivals were on separate levels, to give travellers a clear sense of direction; ticketing and the departure lounge were under the tracks. The project covers 60,000 m².

For the reopening, AECOM and Weston Williamson + Partners linked the terminal to Waterloo's main concourse with a new link bridge and an infill roof over the Underground, and brought the spaces under the tracks up to current standards, adding shops there. They carried on the original details: glazing, ceiling panels, concrete finishes.

Platforms 20 to 24 are now platforms of Waterloo station, served by suburban trains. Under the tracks, the lower level of the former terminal forms a concourse linked to the platforms by lifts.

Waterloo station closes overnight. Like every platform in the station, platforms 20 to 24 are behind ticket barriers; all of them can be reached step-free from the main concourse.