You might feel comfortable at home, but would you feel so snug if you knew what was going on just beneath it? Some years ago, residents of a street in Harold’s Cross were horrified when their front gardens suddenly sank 10ft. The accident happened when a little-known tunnel running under hundreds of Dublin properties collapsed.

If you live in an older part of the city, it’s quite possible your home is accessible from the many forgotten tunnels and cellars below. If you live in Ranelagh, Rathmines or Dublin 4 in particular, it’s quite possible an army could march under your home, and during the war of independence and the civil war, it’s quite possible they did.

Dublin city council worker David Greene sees a side of Dublin city centre that others seldom do. Underground, he strolls from St Patrick’s Cathedral to Temple Bar and finally comes to a halt on the quays where he takes time to peer into the River Liffey. Greene has walked about a quarter of a mile through some of Dublin’s busiest spots and has not seen a sinner. He is one of only a handful of people to have walked this route in 100 years. Some were Michael Collins’s rebels, or more recently bankrobbers on Dame Street.

Greene walks through one of the vast tunnel complexes under Dublin city. In this case, he has strolled along the River Poddle culvert in which you can walk upright for almost three miles from Harold’s Cross to the Liffey.

“People don’t think of these tunnels until something happens to them,” adds Greene.

“Householders in Harold’s Cross were surprised to find their front gardens seemed to vanish into the ground. In fact the Poddle tunnel had collapsed.”

Along with the Poddle, the Camac, which runs from through Bluebell and Inchicore, and the Swan, which runs through Dublin 4, Rathmines and Ranelagh, also have extensive pedestrian-worthy tunnels.

The Poddle, once an important river in Dublin city along with the Swan and the Camac, is now covered over. Once enough to bring on a torrent for Dublin’s black pool (Dubh Linn), the Poddle is a sorry trickle which, unless it has been raining heavily, can be walked.

“Dublin people walk around every day without realising there’s a whole forgotten world under their feet,” says Greene, who loves his job in the city’s drainage division. “You can walk for miles without coming up.”

If there are any worries, it’s from the card-carrying members of the rat race. “We’re entering the kingdom of the rats. This is their world. But they’re as afraid of you as you are of them,” he says.

The Poddle is one of many tunnels that was used by rebels to outfox the authorities and then to outrun one another in the two wars that saw the founding of the state.

Greene, the Poddle tunnel and all manner of matters underground in Dublin are the subject of Thursday’s Leargas programme on RTE.

The programme deals with the Poddle, as well as the old Phoenix park rail tunnel, which isn’t used for passenger trains although it connects Heuston and Connolly Stations.

According to producer Fachtna O’Drisceoil, the programme will show the first camera footage taken in many of these seldom-seen underground locations.

“Many of Dublin’s older houses have plenty going on in the basement and beyond, but much of it has been long forgotten, either because entrances have been covered up or because office-users simply never look there,” says O’Drisceoil.

Featured in the programme is a recently discovered medieval slipway which has recently been found in the basement of a house at Merchant’s Quay. The slipway is much the same as it was 700 years ago. The most recent surprise, however, unearthed under a modern building, is presently in the charge of archaeologist Linzi Simpson. Dublin’s original poorhouse, long lost to the city, was recently unearthed in excellent condition under a more modern building at St James’s hospital.

Most recently the Dublin Port tunnel is making its way unnoticed under hundreds of Dublin properties with the largest tunnelling machine ever used in Ireland.

Most of the old houses in the Temple Bar and Dame Street areas have complex cellar systems, some of which are used as bars and nightclubs today, but still many more remain unprobed, stretching in front of, next to and behind their own buildings. So be warned before you venture beyond the cellar door — you never know what you may find.

Dublin Leargas is on RTE-1 on Thursday at 7pm

Explore Property

• Buying & Selling

• New Homes

• Overseas

• Interiors

• Investment

• Gardens

• Cool In Your Code

• Specials

• First-time buyer

• Rental Market

Times recommends

• Second homes: credit crunch casualty or money-spinner?
• How I built my own sliding house
• Top 10 incentives for house buyers