ArcelorMittal Orbit

Stand at the base and tilt your head back. Above you, a red steel tube twists and loops into the sky, curling back on itself like a rollercoaster that forgot where it was going. On a breezy day you may hear the wind moving through the lattice. On a busy day you will hear something else: the distant, rising shriek of someone hurtling down a slide wrapped around the tower. Welcome to the ArcelorMittal Orbit, in Queen Elizabeth Olympic Park in Stratford, east London.

This is the tallest sculpture in Britain. It stands around 114 metres high, a little taller than Big Ben. But height is only part of the story. Look closely, and you will see that the structure does not rise in a straight line. It climbs, bends, crosses over itself, and climbs again. There is no clean front or back. Walk a slow circle around the base, and the shape changes with every few steps you take.

The Orbit was built for the London 2012 Olympic and Paralympic Games. It was designed by two people working together. One was Anish Kapoor, the Indian-born British sculptor. He is also known for the giant mirrored bean in Chicago's Millennium Park. The other was Cecil Balmond, a structural engineer famous for designs that seem to defy ordinary rules of geometry. Kapoor brought the sculptor's eye. Balmond brought the mathematics that keeps this tangle of steel standing.

Here is a detail many visitors miss. The structure is not a tower with decoration added to it. The red loops are the structure itself. Balmond's idea was a kind of endless, unstable orbit, where the lattice carries its own weight as it spirals upward. Only the central core, which holds the lifts and stairs, behaves like a conventional building. Everything else is a continuous ribbon of steel, bolted and welded into a shape that looks almost improvised.

The name comes from the steel company ArcelorMittal. Its chairman, the industrialist Lakshmi Mittal, provided most of the funding, and the company supplied much of the steel. A large share of that steel was reportedly recycled. The project was championed by Boris Johnson, who was then the Mayor of London. He wanted the Olympic Park to have a landmark that people would remember long after the Games had finished, and that would draw visitors back to Stratford.

Not everyone loved it. When the design was first revealed, critics compared it to a tangled coat hanger, a giant trombone, or a helter-skelter that had collapsed. Some people found it ugly. Others found it thrilling. That argument has never fully ended, and perhaps that is the point. Public art that nobody talks about is quickly forgotten. Whatever you think of the Orbit, you will probably have an opinion about it before you leave the park.

Now look around you at the wider landscape. Less than two decades ago, this ground was very different. The Lower Lea Valley was a patchwork of industrial yards, railway sidings, and polluted waterways. Before the Games, the land was cleared and cleaned on a huge scale. Rivers and canals were restored. Wetlands and meadows were planted. The park you are standing in today is one of the largest urban regeneration projects in modern British history.

From the base, you can pick out some of the park's other landmarks. The large oval nearby is the London Stadium, the main Olympic venue. It is now the home ground of West Ham United football club. Close by is the London Aquatics Centre, designed by the architect Zaha Hadid, with a roof that curves like a wave. Since the Games, new neighbourhoods, a university campus, and cultural buildings have grown up around the edges of the park.

Inside the Orbit, a lift carries visitors up to the viewing levels near the top. From there, on a clear day, the view runs right across London. You can look west towards the towers of the City and Canary Wharf, and pick out the curve of the Thames. Inside the viewing gallery, look for Kapoor's large concave mirrors. They bend and flip the skyline, so the city appears upside down. Many people find themselves photographing the reflection rather than the view.

If you prefer to come down on foot, there is a staircase that winds down through the structure. It is a long descent, with several hundred steps. Walking it gives you a very different sense of the Orbit. Instead of looking at the red steel from a distance, you are moving inside it. The loops pass close beside you, and the park below slowly grows larger with every turn of the stairs.

Then there is the second surprise. In 2016, a slide was added to the tower, designed by the artist Carsten Höller. He is known for turning slides into works of art in galleries. At its opening, it was described as the longest tunnel slide in the world. It wraps around the Orbit many times, through bends and a corkscrew, and the ride down takes less than a minute. Parts of the tube are clear, so riders catch flashes of sky and city as they fall.

That slide changed how people use the Orbit. Before, it was mainly a place to look at the view. Now it is also a place to scream, laugh, and come out at the bottom with your hair in a mess. Watch the exit for a few minutes. You will see children jumping up to go again, and adults who look slightly shocked. Art and a fairground ride now share the same structure, and somehow that feels right for this playful, strange sculpture.

Before you go, step back and take one more look. Notice how the red colour changes with the weather. Under grey London cloud, it looks deep and almost brown. In low evening sun, it glows. The surrounding trees and meadows soften the industrial steel. The Orbit was built for a single summer of sport, and it remains here as a reminder of that moment.

As you walk away, glance back over your shoulder every so often. From each new angle, the loops line up differently, and the tower seems to twist again. Listen for the trains on the nearby lines, the voices from the stadium, and the water moving through the restored channels of the River Lea. This part of London has changed completely in a few short years. The red steel in front of you is one of the clearest signs of that change.