The Channel Tunnel has been described as one of the wonders of the modern world, a remarkable infrastructure project which cost billions and was delivered by more than 13,000 workers.

As the tunnel celebrates the 30th anniversary today, operator Eurotunnel invited reporter Rhys Griffiths to take a look behind the scenes…

“You're playing with one of the world's biggest train sets here?”

It’s a throwaway quip lobbed in the direction of controller Kai Herbert as he shows me around the impressive Rail Control Centre at Eurotunnel’s terminal outside Folkestone.

“Some people look at it that way, but it's a bit more serious than that,” he retorts, returning my semi-serious gambit with an impeccably straight bat.

And he is right. The work being done at the RCC here in the UK, and at a mirror facility across the water in France, is extremely serious. From these workstations at either end of the Channel Tunnel, staff can oversee the operation of the entire network down to the smallest working parts.

“We can turn light bulbs off and on in some room in the middle of nowhere in the tunnel,” Mr Herbert says as he guides me past each of the posts in the cavernous control room.

“I think there's something like 40,000 sensors that arrive here.”

Another statistic. Just one of many numbers you can reel off to illustrate the sheer scale and complexity of this undersea railway linking Britain and France.

The Channel Tunnel stretches for 32 miles between its two terminals, one at Folkestone here in Kent and the other at Coquelles in the Pas-de-Calais. The undersea section itself runs for 25 miles, making it the longest undersea tunnel in the world. At its deepest point, the tunnel is 75 metres below sea level.

In all more than 13,000 people worked on the remarkable construction project to deliver this fixed-link across (or should that be under) the Dover Strait, the final bill for the building of the tunnel coming in at a staggering £4.65 billion.

People had dreamt up all kinds of schemes for a physical link across the Channel for centuries, but it was only in 1986 with the signing of the Treaty of Canterbury that those dreams were finally set to become a reality. The work of digging the Channel Tunnel started in December 1987 from the UK side, and in February 1988 in France. It officially opened on May 6, 1994 - 30 years ago today.

Tunnelling can be a dangerous occupation and 11 workers, eight of them British, were killed during construction - most during the first few months of boring. In recognition of the risks involved, they were paid about £800 a week - equivalent to £2,038 a week today.

We may talk about ‘the tunnel’ but in fact the Channel Tunnel is made up of three separate tunnels – two single-track rail tunnels and a smaller service tunnel.

The two main ‘running’ tunnels are 7.6m in diameter and 30m apart. Each has a single track, overhead power line, and two walkways, one for maintenance purposes and the other for use in the event of an emergency evacuation.

Sitting between the two rail tunnels is the service tunnel, just 4.8m in diameter and connected to the main tunnels by cross-passages every 375 metres.

Not only is the service tunnel an access route into the tunnels for maintenance crews, it also provides a vital path to safety should anything go wrong underground. For this reason, it is kept in a state of air overpressure so that it remains safe from fumes in case of fire in one of the railway tunnels.

As part of my exploration of this engineering wonder of the modern world, Eurotunnel has granted me the rare opportunity to enter the service tunnel for a look around.

Although I have in the past zipped through the Channel Tunnel on tourist Le Shuttle trains, as a Eurostar passenger, and even once on board a freight Shuttle, it is a strangely exhilarating moment to enter this underground world by car.

Quite rightly there are security and safety protocols to be followed, so it’s on with the high-viz and the sturdy boots, and passes and biometrics have to be scanned before we can cross the threshold of the tunnel itself.

Soon enough the huge metal doors which seal off this closely-controlled environment begin to slowly swing open, and our tiny Fiat Panda plunges into the tunnel.

Our driver, aware of a first-timer on board, casually remarks how some people react badly to the claustrophobic nature of this space, with its 4.8m diameter and 32 miles until you re-emerge into the light of Coquelles. But the confined nature of the space isn’t what strikes me - instead I am lulled by the hypnotic feeling brought on by the monotony of the tunnel’s featureless interior as we move ever further inside.

Our trip is only to be a short one, anyway, heading as far as the point where the tunnel boring machines which dug from the British side were lowered into position. Reaching this point of the service tunnel, I get out for a quick walk around, marvelling at what an incredible feat of engineering this whole project was.

Directly above our heads at this point is Samphire Hoe, the coastal nature reserve which was created from nothing. Some 4.9 million cubic metres of chalk marl and shale which emerged during construction on the UK side – apparently enough to fill Wembley Stadium seven times over - were dumped here.

After our driver pulls off a very nifty three-point turn (it is very, very narrow down here) we’re soon enough zipping back towards the tunnel mouth and the light of an overcast Folkestone afternoon, which still hits you after a spell in this artificially-lit subterranean world.

It is not the busiest of midweek afternoons, so we are free to pay a visit to the Traffic Control Centre where the above-ground operations of the UK terminal are overseen. While the RCC we visited earlier is all about the rails and the underground infrastructure, here the teams are dedicated to keeping the terminal and, as best they can, the surrounding road network moving.

I am shown around by Sara Crowther, who is supervising this afternoon’s shift. Unlike in the RCC, where staff have to rely on diagrammatic representations of the activity in the tunnels, here in the TCC staff have huge windows and an array of monitors which allow them to see everything happening in the 150-hectare terminal.

“We're monitoring the system to make sure the trains are leaving France on time, so we can anticipate reloading them on this side,” Sara tells me when I ask about her day’s work.

“We have an operations manager and at the beginning of each shift they will give us a strategy, and today it's to maintain the timetable.

“Which means if a train leaves France late we have to get it back on time. It's imperative we do that because there's quite a lot of trains in the tunnel at one time, with freight, tourist and Eurostar, and if one goes late it impacts the next four.”

Lots of moving parts in this giant train set, and it’s no good running those trains perfectly unless you can make sure the right passengers and freight are loaded onto the right Shuttles at the right time.

Eurotunnel carries almost 10 million passengers a year, as well as more than a million freight trucks. And that’s before you take into account those using Eurostar high-speed train services from London to reach the likes of Paris, Brussels and Amsterdam.

No wonder the Channel Tunnel is rightfully considered one of the wonders of the modern world.

Visit KentOnline tomorrow for a look back at what life was like in east Kent before the Channel Tunnel - and how much has changed since.