"If you look far back into this one, you'll see something glittering on the walls," says the tour guide, waving his industrial torch in the vague direction of infinite darkness. "It's not gold, it's left over from when the BBC filmed Doctor Who here."
For anyone playing pop culture bingo, that's the second tick that Chislehurst Caves offers — the first being a reference to the two times that Jimi Hendrix played among the chalk caverns, 30ft below the streets and homes of Chislehurst. A rickety old bar remains, its alcohol offerings long since replaced with chalk dust and cobwebs. It's a testament to the launch party of Led Zeppelin's Swan Song Record Label, which happened in the caves on Halloween 1974.
Like most of London's subterranean offerings, Chislehurst Caves are entirely manmade. Originally used as flint and chalk mines, there are unsubstantiated rumours that they've been around since Roman times (or before) but most people are reluctant to believe this.
The caves came into their own during both world wars. Ammunitions were stored here, below the streets of Chislehurst (an overflow from storage at Woolwich Arsenal) during World War One. Most famously though, 15,000 people took shelter in the caves during World War Two. Swathes of people from London and Kent paid 1p a night to sleep in the biggest bomb shelter in London. The incomprehensible maze housed not only thousands of beds, but had a whole hospital wing and other facilities.
So many people packed into the caves when they were used as bomb shelters that the temperatures often reached upwards of 70°F, something that's hard to imagine today — even on a stuffy August day, you can see your breath in the cold surrounds.
Along with the significant temperature drop, a pungent smell overpowers when you enter the gently-sloping concrete corridor leading down to the caves. It's a world away from the overgrown brambles which climb through the glassless windows, a last link to the outside world before darkness descends.
Lanterns are available to adults. Take one. Even beady-eyed visitors who need no assistance to see will benefit from the warmth a lantern offers as they descend deeper into the subterranean warrens. The walls, whitewashed in some places, naturally coloured in others, are indeed made of a soft chalk — a clandestine poke with a sharp finger nail confirms this. In parts they're heavily dotted with the flint which once made the caves so profitable.
A 45 minute whistle-stop tour covers just one mile of the 22 available. A vast cavern with a dome, once a chapel, is now off limits to the public thanks to an invasion of tree roots from the world above through the chalky ceiling, causing occasional crumbling. A well has recently been brought back into action. An underground pond lays claim to the predictable haunted story. A shaft in the ceiling leads directly into the garden of an unsuspecting Chislehurst resident.
Brisk though our tour guide is, we wouldn't fancy being down here alone, despite reassurances that no-one ever died in the bomb shelter (one baby was born though). The winding corridors, echoey chambers and rough ground all begin to look the same within a few minutes, and beyond the electric-lit tour route, it's pretty dark and dingy. Just as the cold becomes almost unbearable, we return to the old entrance hall and ticket office, where those wartime residents paid their entry fees.
Emerging through the double doors and blinking in the daylight, the relative heat is welcome. The chilly air and stuffy smell that we've adjusted to are quickly forgotten as we brush the chalk dust off our jacket and return to 21st century life.
The ticket office where the tour begins and ends houses a small gift shop and a cafe. It's reminiscent of an old fashioned railway station waiting room with tall ceilings, wooden benches and historic photographs of the local area adorning the walls. A wall-mounted TV offers an interesting-looking glimpse into local history but the sound is so quiet that learning about it is sadly not an option.
If you're looking for somewhere to rival the stalagmites of Wookey Hole or Cheddar Gorge, you may be disappointed with the manmade Chislehurst Caves (but Painshill Park in Surrey has a crystal grotto which may be more up your street). Very young Londoners or those who are easily scared probably won't enjoy a trip to the caves, but for anyone else, it's value for money and an unexpected insight into the local history of this corner of London.
Chislehurst Caves, Caveside Close, Old Hill, Chislehurst, BR7 5NL. Entry is £6 adult/£4 child. Check website for opening hours and tour times.