In a flat corner of western Germany, not far from the Dutch border, a giant concrete tower rises over a small, cheerful fairground.
The tower is painted with a bright alpine mountain, and inside it a swing ride lifts shrieking children in slow circles.
It feels like any other theme park, a little dated, full of families spending a sunny afternoon.
From the entrance it looks cheerful and faded, the kind of place a family visits once and forgets.
But that tower was never built for fun, and what it was built for is almost impossible to believe while you are standing under it.
The strangest fairground in the country
The place is called Wunderland Kalkar, and on a busy day it draws thousands of visitors.
Around 600,000 come every year.
There are roughly forty rides, half a dozen hotels, go karts and a ferris wheel.
Most of the halls and towers here are not stage scenery but the original structures, simply cleaned up, repainted and reopened.
The signature attraction is the swing ride bolted inside that towering concrete cylinder.
On the outside of the very same tower, someone has fixed a climbing wall.
Children scale the curved grey shell while a painted mountain smiles down at them.
And almost nobody stops to ask why the tower is there at all.
Far too big for a playground
Step back, and the scale stops making sense.
The whole complex covers something like eighty football pitches.
It holds enough concrete to lay a motorway from Amsterdam to Maastricht, and enough cabling to wrap around the planet twice.
The buildings are vast, windowless and impossibly solid.
No fairground needs walls like these.
Whatever this place was meant to be, it was designed to run for decades, around the clock.
This site was poured and wired for something enormously more serious, at a cost that still stings to read.
And then, after every last piece of it was finished, the job it was built to do simply never happened.
A fortune spent, and then abandoned
Construction began in the early 1970s and dragged on for more than a decade.
The budget started at a couple of billion and kept climbing, year after year.
Long before it was done, the project had become a national argument.
In 1977 around forty thousand people marched through the small town in protest.
The first budget had been set at little more than two billion marks.
The works were halted, redesigned, restarted and halted again.
Safety worries forced parts of the design to be torn up and rebuilt more than once.
By the time it was technically complete in 1985, it had swallowed about seven billion Deutsche Mark.
That is roughly the price of twenty thousand houses, spent on a building that would never switch on.
What the tower was really built to do
The complex is the SNR-300, a nuclear power station, and not an ordinary one.
It was a fast breeder reactor, a rare and ambitious design meant to make more plutonium fuel than it burned, cooled not by water but by liquid sodium.
That painted cylinder is its cooling tower.
On paper it was designed to feed 327 megawatts into the German grid.
Three governments, in Germany, Belgium and the Netherlands, had backed the dream together.
It was one of the boldest energy bets of its era, a cousin to other huge projects pushed to the edge of what engineers believed was possible.
Then in April 1986 the reactor at Chernobyl exploded.
Public fear, the danger of sodium and the spiralling bill convinced the regional government to block it, and in 1991 the SNR-300 was cancelled without ever being loaded with fuel.
From the most expensive ruin to a swing ride
For a while the finished reactor simply sat there, too costly to run and too poisoned in reputation to love.
Then a Dutch entrepreneur bought the site for a tiny fraction of what it had cost to build.
He left the great structures standing and wrapped a holiday park around them.
The hotels opened in the late 1990s, and the rides followed in the years after.
Today it pulls in around fourteen million euros a year from the visitors who wander its strange grounds.
The tower that was meant to vent the heat of a plutonium reactor now spins a fairground swing instead.
It is hard to call it a clean happy ending, given the fortune that vanished into the concrete.
But there is something fitting about it, a monument to an energy dream that failed, remade into a place where children laugh.
The reactor never produced a single watt.
The swing ride, somehow, has never stopped running.