THE Mersey Tunnels are something millions of motorists on both sides of the river take for granted every year.
According to Merseytravel, an estimated 25 million vehicles pass through them every year, carrying around 37 million passengers.
A new behind-the-scenes tour of the Queensway Tunnel gives the public a chance to find out what goes on beneath the Mersey.
Frank Rogers, Merseytravel’s deputy chief executive. said the aim of the tour is to raise awareness of how the tunnels operate.
All funds raised from the tour are used to pay the tour guides.
An interesting fact is that in case of emergency, there are seven refuge rooms for motorists under the roadway of the Queensway Tunnel.
The rooms are kept well-lit, have seating, and supplies of bottled water.
They're linked to a control room at Wallasey police station. The rooms have only been used once, in 2012, when a vehicle caught fire.
Mr Rogers said safety is of paramount importance when people are in the refuge areas: "When you open a door you are directed along to another refuge, because we wouldn't want you to end up in a dangerous place like a pump system.
"The last thing you want in the refuge room is for the lights to go out.
"So we have a have a back-up uninterruptable power supply. The fan room is also said to be home to the ghost of a engineer who died in the 1950s."
Alison Smith, tunnel tour guide, said: "We call him 'Gillie the Ghost'.
"There's a story that he walked past a member of staff one night, dressed in 1950s' clothes.
"When the member of staff turned round, the man had gone.
"I've actually done this tour for seven years, but have never seen him yet."
Queensway, which links Birkenhead to Liverpool, opened in 1934; Kingsway in Wallasey opened in 1971.
The tunnels have 5,428 light fittings.
44 fans, eight ventilation stations, 30 pumps to remove ground water and 11 standby electricity generators, with capacity to power 2,700 homes. The electricity bill is £1m a year.
There are also 400 CCTV cameras linked to a central control room to assist in assessing traffic flow and in the event of accidents and emergencies.