Construction of the Large Hadron Collidor, a giant underground particle accelerator, is reaching a major milestone as a key piece of machinery is lowered into the ground. BBC News Science Correspondent David Shukman reports from the scene.
YB0 is the biggest and most impressive element of the CMS
It's like stepping onto the set of a James Bond film.
Or possibly something involving Austin Powers.
Everything here is on a vast scale; many tens of thousands of cables woven together, silicon sensors by the thousand, towering shapes of steel, impossibly complicated engineering and science.
I'm in a building the size of a hangar. At one end stands a giant circular component, 15m (50ft) across, an intricate assembly of red and silver. Teams of workers clamber over it, inside it.
At the other end, a huge chunk of concrete floor is missing, slid away to open access to a shaft reaching 100m (300ft) down to a vast cavern.
Right now, the largest component of a new detector, the Compact Muon Solenoid (CMS), is being lowered down the shaft and into position for final assembly underground.
Four dense bundles of steel cable are straining under the weight of nearly 2,000 tonnes. Engineers in hard hats keep close watch as the precious instrument slips below at the barely observable speed of 10m (33ft) per hour.
This is where the worlds of theoretical physics and heavy engineering collide.
Ideas dreamed up on academic blackboards two decades ago are now materialising as tangible high-technology.
A noble idea
Is it all worth it?
The objectives are noble - to understand the innermost workings of the universe. There's so much that we don't know: only a few percent of the universe is made up of what we know to be matter, the rest is unexplained. This project may provide answers.
But don't expect immediate spin-offs. This is science at its most fundamental.
If everything works, if the beams of particles successfully collide, if the detectors do their job, if the researchers can make sense of the reams of data that will flow from these machines, then we'll be able to say if the £2bn (3bn euros) was wisely spent.
I go to the chasm to check on progress.
A fence keeps me back from the edge. The cables are as taut as ever, the massive component is now well below ground. Our remotely-controlled camera in the cavern below shows the dark shape blocking most of the light in the shaft.
So far, everything is on course.