The AutoTürme are the reason people photograph the place. Two cylindrical towers of glass, each 60 metres tall, stand at the water's edge holding finished cars on stacked circular racks - visible from outside, lit at night, more aquarium than warehouse. A 700-metre tunnel runs beneath the canal from the factory, so a car reaching a tower has still never touched a public road. An automated lift rides up the central column at 1.5 metres per second to pluck out the right vehicle. Customers who choose to collect in person get free entry to the park, meal tickets and a build-up of small ceremonies, ending with a screen on which they watch the mechanism find their car and bring it down. The car is then handed over having never driven a single metre outside the works.

The idea started in 1994, out of a plan to document how Volkswagen vehicles are made and to show the company off at Expo 2000 in Hanover. Ground was broken in 1998 on the former site of a fuel company bordering the plant, and the finished complex is credited to more than 400 architects working under the Munich practice Henn GmbH. The investment came to roughly 850 million Deutsche Mark. What they produced is not a museum with a car park but something closer to a small district: pavilions scattered across landscaped ground, lagoons and channels of water threading between them, grassed earth mounds shaping the sightlines, and benches and chairs designed with the same seriousness as the buildings. It was conceived as a new urban centre for a city that had never been given one.

Each brand in the group gets a building that argues its case in architecture. Volkswagen has two - a large circular pavilion covering more ground than any other, showing the current range across two floors, and a much smaller production pavilion added late. The Porsche pavilion is entered down a curving descending corridor into a single quiet hall holding a Boxster, a 911 and a Panamera, with scale models of earlier generations ranked behind them. The Premium Clubhouse, renamed in 2008 from the Bentley pavilion and now shared with Bugatti, is buried in a grass mound under a marble roof, its displays including a chrome-finished Bugatti Veyron. Škoda's pavilion is built around metal sculpture. The Lamborghini building is entirely black, and its show begins with an orange Aventador fixed to the wall, which vanishes into dry ice and reappears, upside down in effect, mounted on the outside of the building.

The Audi pavilion hands each visitor a small plastic sphere, activated at the entrance with a name and a photograph. As you move through the building the sphere glows in the colour of whichever section you are standing in, and pressing it into hemispherical depressions on the walls triggers things: a technical film, a real headlight illuminating behind glass, floor lights that mime an electric car charging. Drop the sphere in a collecting pit at the end and your photograph can be emailed on. The SEAT pavilion, one of the largest, sits in water and planting, reached across a bridge under a glass roof, with one entire wall built from red wing mirrors. The exit bridge rests on metal tubes containing speakers, and every footstep across it fires off a castanet click - a nod, in a German industrial park, to the Spanish marque's home.

Under the bridge that carries visitors over the canal from the town, the Autostadt keeps an off-road course for the Volkswagen Touareg. Show a driving licence and a guide will first take you round it, narrating what the vehicle can do, then swap seats and let you drive with the guide beside you and any passengers in the back. The course includes a 21-degree climb, a hill cambered hard to one side, a water hazard, a sand pit tucked beneath a road bridge, a log road and a scatter of mounds designed to lift one wheel clear of the ground. Children get their own circuit and small electric cars shaped like Beetles. Elsewhere there is a room comparing what different fuels do to a car's performance, design software that lets visitors build their own vehicles, two cinemas showing short films in German - one of them inside a large sphere - and a museum holding some genuinely important machines, including early petrol vehicles and the Beetle that started all of it a few hundred metres away.