IT is one of Southampton’s iconic landmarks and a major route in and out of the city.

The Itchen Bridge has towered above the River Itchen for almost 40 years.

And in the first of a new series of Hidden Hampshire features where the Daily Echo has teamed up with Solent TV, Southampton Solent University's award-winning entertainment and documentary web channel to take readers to parts of the county they couldn't normally go, we are taking a look inside the iconic structure.

During the four decades it has towered over the Itchen millions of vehicles have travelled over it – paying around £80m in tolls.

But one of its biggest secrets is that people are actually able to walk inside.

So when civil engineer John Simpkins, who looks after the 62,000-ton bridge, offered me the chance to go where no Echo reporter had gone before and look around I couldn’t resist.

We stepped into an enormous cavity which lay just a few feet under the asphalttarmac.

The lights flickered on and a huge corridor of thick concrete stretched out in front of us as lorries thundered overhead, clattering across the joints of the bridge.

It was as if we had slipped inside another world, away from the hustle and bustle of the city.

John explained that the cavity inside the bridge is normally out of bounds to the public and it is rare that even workers go inside.

The main reason people step under the road is for bridge inspections, which take place at least once every six years.

A team of specialist engineers walk below the carriageways to check the structure is still in good condition and make a note of any maintenance work that needs to take place.

Meanwhile, a team on boats check the pillars soaring 23m above the river and specially-trained divers are sent to check the cofferdam, the part of the structure below the fast-flowing waters.

Although the bridge is owned by Southampton City Council, inspections and work are normally carried out by Capita.

“You do get pressure to try to keep the impact of your work to an absolute minimum and some times you have to cause some disruption. It’s inevitable,” said John.

“It’s important to do maintenance. I think everyone understands that.

“If you don’t do it early you could have some pretty big consequences. I’m happy to say we don’t have anything anywhere near close to that at the moment.”

The last inspection took place in February and earlier this year the bridge was closed overnight for maintenance work.

Workers replaced expansion joints which had been there for more than 10 years.

John’s role at Capita involves overseeing work on the highway’s structures including inspecting, maintaining and managing all of the city’s highway’s bridges, culverts, retaining walls and subways .

The dad-of-three from Sway became a civil engineer 17 years ago and has been looking after Southampton’s bridges since 2004.

Although he has always been interested in engineering his passion for bridges only began while he was studying at the University of Southampton.

“I have always been a little bit interested in engineering. When I was younger I didn’t get into bridges until I went to uni,” said John.

“It’s an area of work that you get to use lots of skills that you’re good at. Either physics or maths.

“It’s interesting work because it’s so varied. I like telling people what I do.

“I do tend to look at bridges when I’m on holiday with the family.

“I have got a little boy now so he’s much more interested in that sort of thing, whereas the girls aren’t so much.”

But he says he feels a degree of ownership for the bridges he looks after in Southampton.

John said: “It’s got a bit of grandeur. People do see bridges. They’re all landmarks.

“I feel a degree of ownership with the structures that we look after.

“This bridge is clearly very strategically important to the city.

“It’s certainly visible. It’s an important local link.”

We walked to the end of the echoey tunnel and crawled through a small gap into the next section of the bridge.

We were now stepping over the water as cars rushed overhead.

We passed a well and John explained it went all the way below the river and deep into the foundations of the bridge.

At the end of the next tunnel was a wall, fenced off with chicken wire to stop the roosting pigeons from getting in through the gaps.

John said we had reached the very centre and this was as far as we could easily walk.

As we headed back to the entrance he told how during inspections workers would walk through the cavity from both sides, stopping at this middle section.