Flaring its muscular grey wings like a stingray leaping out of the river Lea, the Aquatics Centre was planned as the showpiece of the London 2012 Olympic Games, a piece of liquid drama designed by the country's most celebrated queen of the curve, Zaha Hadid.
Its signature swoop would make up for the austerity of the flat-pack stadium and distract from the lunacy of the Orbit sculpture and the tacky fields of temporary marquees. Yet for the two-week event its lithe body was trapped between two hulking great seating stands, as if they'd forgotten to remove the scaffolding. If this was the belle of the ball, she was a debutante in dental braces.
"I didn't mind the seating stands so much," shrugs Hadid, sitting poolside beneath the bulging belly of her building, which finally opens to the public on Saturday. "They served their purpose, and it was always planned for what would come after: providing a great new public swimming pool for east London."
Now liberated from its armbands, the building floats effortlessly free, its roof dipping and diving between two vast walls of glazing that provide views straight through to the park beyond. Gaggles of children from Newham's nearby schools, visiting on Tuesday for their first splash, couldn't be more thrilled. "It's like swimming in a spaceship," says one before leaping off a diving board which erupts from one end of the pool like a thick concrete tongue. "I can't believe we'll be having our swimming lessons here."
The complex houses two 50-metre pools. In the training pool area, conceived as a cave-like space with a beautiful coiffured concrete ceiling, a 40-metre-long inflatable assault course is being put through its paces. Both pools are equipped with sliding booms and movable floors, meaning there can in effect be up to six swimming areas in operation at once.
"It's the most spectacular space I've ever swum in," says a swimmer emerging from a tumble turn. "It's fantastic to be flooded with so much natural light and have a view of the stadium and the changing skies as you swim. Doing lengths here will never get boring."
Rising up from a single point at its southern end, the roof hangs in the air, its continuous timber skin belying the structural gymnastics going on inside it, where 3,000 tonnes of steel zigzag their way unsupported for 120 metres in a dense network of trusses. Eyebrows were raised at the sheer amount of material (and the £269m cost, which rose threefold from the initial budget), particularly compared with the stripped-back velodrome, which uses only 100 tonnes of steel cable to cover a similar area.
"What do the critics know about how much steel should be in a roof?" says Hadid. "Besides, we had to have uninterrupted spans for these open side windows, and we're building over two tunnels and next to the river. It's an incomparable project."
The tricky site, sandwiched between waterways, railway lines and vast elevated concourses, means this alien object isn't quite as elegantly resolved outside as within. The everyday entrance sequence remains a clumsy switchback route that entails overshooting the glazed prow of the building (only used for big events) and descending a staircase to what feels like a service entrance below.
To the south, where the ground rises up to meet the roof, the transition is made with an odd grassy berm and green wall, the default option for hiding some air vents.
But once inside it is hard to fault, from the sculptural concrete curves that yawn open to provide views between the pools to the drama of standing on top of the diving boards, with London's skyline framed by the sweeping roof. Not bad for £4.50 a go.