The follow-up to an account of life below London finds underground marvels all over England. E&T met the author.
Almost 40 years after the Apollo 11 mission took people as far as they've been able to travel and return to tell the tale, it's worth remembering that even the most developed countries on terra firma have places that have been barely explored. You just need to look under your feet.
"There are remote parts of Yorkshire cave systems where fewer people have stood than have walked on the Moon," points out Stephen Smith, who with the publication next month of 'Underground England' continues the theme begun in his 2004 bestseller 'Underground London'.
Smith's fascination with the subterranean began as a kind of aversion therapy when he returned to the capital to work for Channel 4 News after a spell living in the wide open spaces of the Yorkshire countryside.
"I found it a real culture shock to be on the London Underground in the mornings. I was semi-phobic about it and would try to stand by the door or the window. At the same time I was looking at the tube map and comparing it with the A to Z, thinking it's great but it doesn't tell us much about what's down here."
His solution - spending nights in the tunnels with maintenance crews and travelling alongside drivers in the cabs of tube trains - prompted a fascination with the relationship between the streets we're familiar with and the world below the city.
"You think you know a place on the surface but there's so much going on underneath that you wouldn't be conscious of. I like that sort of continuum. We're used to thinking this building is next to that building, which is next to that building, but what about what's underneath it?"
The answer, in many cases, is some sophisticated engineering. Take the Victorian coal wagon tunnel running under the centre of Newcastle, which Smith explores in his new book. Built so that coal could be transported to the city's docks without clogging up the streets, it remains in good condition. But because it's out of sight it's simply never established itself as a landmark in the public consciousness.
As Smith says: "You can be standing by a discount warehouse and the tunnel's below you, but no one would know."
Smith is regularly seen on TV in the UK in his role as culture correspondent for the BBC's 'Newsnight'. The son of a civil engineer, he admits some of his interest in 'hidden' engineering can be traced back to childhood holidays in Scotland which were punctuated by trips into the countryside to see the remote dams his father had helped build.
And while some of the places he visited around the country are natural features that have been exploited over the years for practical, or in the case of caving, recreational, purposes, there are many that represent outstanding feats of engineering.
At one extreme are the tiny priest holes built into Catholic homes in the 16th century to provide a place where visiting clerics could conceal themselves for days at a time. "They're really ingenious. The James Bond stuff of their day," says Smith.
At the other are huge projects like the 1.5 mile Mersey Tunnel in north west England, the military complex dug below Dover Castle in the south east during the Second World War. Smith went behind the scenes at both, and at the Millennium Seed Bank at Wakehurst Place in west Sussex where botanists are taking advantage of the fact that temperature and humidity can be more easily controlled underground to create a collection of every seed on Earth.
Anyone inspired by the books to venture out on their own explorations might end up disappointed. The tightening up of security prompted by an increased awareness of how vulnerable underground sites are to terrorist attack means the inquisitive member of the public can no longer rely on being able to wander in and out.
"It's all very difficult now," he warns. "When I was doing the London book there were restrictions, and that was before the London bombings of 7 July 2005. Even something like walking through the service tunnel of the Thames Barrier took quite a lot of negotiation because it's obviously a key strategic point."
If there's an up side to the political and economic situation at the start of the 21st century, however, it's that industrial historians are getting more time to work in when excavations unearth something significant. In better times, these "firemen of history" as Smith describes them would have had to act as quickly as possible. "A building comes down and they rush to the scene; they've only got a small window."
The danger of destroying layers of history below the streets of modern towns and cities is in fact a relatively new phenomenon, Smith explains.
"The Victorians were fairly keen on knocking everything down because it was the new age of steam and industry, But they weren't building tremendously deep foundations because they weren't putting up tower blocks. So what is under their buildings to some extent survives. The danger, archaeologists tell me, is that when you look at some of the skyscrapers that are going up today, they need such deep foundations that if there's a bit of a tiny Tudor cottage, there won't be much there after they've finished."
'Underground England: Travels Beneath Our Cities and Countryside' (hardback, RRP £18.99) is published by Little, Brown on 7 May. E&T readers can purchase at a £2.00 discount (free postage within the UK) by phoning 01832 737525 and quoting LB 079.