As two yellow-helmeted electricians rise slowly on a hoist from the cavern floor to check cabling on a huge red magnet, CERN scientist Marc Goulette makes clear he sees cosmic significance in their task.
"When this refit is completed," he says, gesturing across the gigantic Large Hadron Collider (LHC), "we shall be ready to explore an entirely new realm of physics."
The collider is only five years old but, after swiftly finding a crucial missing link to support mankind's main concept of the universe, is now entering a two-year revamp to double its power in the hope of breathtaking new discoveries.
Some scientists predict it will help identify the nature of strange dark matter that lurks around planets, stars and galaxies; others that it might find a zoo of new particles or even catch hints that space has more than three dimensions.
Buoyed by the early success, experimental physicists and theorists at CERN, the European Organization for Nuclear Research housed on a sprawling campus near Geneva, hope more stunning findings may follow as soon as this decade.
To make this possible hundreds of engineers and technicians are preparing CERN's collider - a 27-km (17-mile) subterranean complex of machinery and cables.
By 2015, it has to be made ready to double its power and its reach into the microscopic world of elementary particles that emerged from the Big Bang 13.8 billion years ago.
"It is a giant task," says senior CERN engineer Simon Baird, showing Reuters around the tunnel 100 meters (330 feet) below the Franco-Swiss border at the foot of the Jura mountains. "Every connection must be checked and reinforced during this shutdown."
Just 10 days after the LHC was first fired up in 2008, a helium leak and resulting explosion in the tunnel caused major damage, and repairs took two years.
"We have to be more certain than certain that can't happen again," adds Baird.
Despite the setback, in just over two years of operations - involving 10,000 specialists around the world analyzing the data its particle collisions produced - the LHC came up last summer with the long-sought elementary particle, the Higgs boson.
Beyond Standard Model
That, explained Canadian physicist Pauline Gagnon, "was the final brick in the edifice of our concept of the universe" - the three-decade old Standard Model that fits everything known about how particles, at the base of all matter, behave.
"With the LHC power doubled, we will start looking for what we think is out there beyond that model. And we always hope that something will turn up that no one had ever thought of. The most likely is something totally unexpected."
But among the "known unknowns" to be sought, Gagnon plumps for dark matter - the invisible stuff that makes up some 27 percent of the universe, six times more than the normal material that reflects light and can be seen from Earth or space.
James Wells, a U.S. professor and theoretician at CERN for two years, looks to more exotic versions of the Higgs - the particle whose associated energy field turned matter to mass after the Big Bang, shaping galaxies - and life on earth.
Those, he said, "could lead us to supersymmetry" - a theory, so far unsupported by LHC data, that every elementary particle has an invisible and heavier partner - "and to up to eight more spatial dimensions".
Oliver Buchmueller, an experimental physicist, also hopes to see proof of supersymmetry - popularly known among proponents as SUSY - and of the extra dimensions foreseen in string theory - the idea that particles are no more than vibrating strings.
Could that take science beyond, into the extension of string theory that predicts the existence of parallel universes or a perpetually growing galaxy of universes, unpenetrable one from the other, that cosmologists call the Multiverse?
"Not in our time," says Wells. "But we humans are amazingly creative. One day, if it exists, we will find a way to prove it."