By Nigel Wrench
Diggers of the Underground, BBC Radio 4
The manhole cover was in the middle of a park in the centre of Moscow.
Wading in underground tunnels offers some people peace
"Here we are," said Eugin, putting a small bag down on the grass. "This is where we go underground."
It didn't seem terribly likely. Outside, at 2230 on a summer's evening in Moscow, it is light enough and warm enough for Russians to sit in groups and on benches drinking cans of beer and talking.
All around the park near our manhole cover, that is exactly what they were doing. Now, while they watched, we were about to go underground.
Eugin pulled a peculiar-looking garment from his bag.
"Put these on. The water down there is not very nice."
I began to attempt to pull on a pair of rubber dungarees.
Eugin is 22. He has his own group of "diggers" - the word used in both English and Russian to describe an emerging sub-culture of amateur explorers who attempt to penetrate the secret spaces underneath Moscow.
I'm not sure I'd do it again, but I think I do now understand the appeal of this hidden underground world
Eugin had already shown me spectacular images on a laptop computer of one of his most extraordinary adventures. He told me they were of a journey along the entire length of a secret underground railway system, first built to evacuate Soviet leaders from the Kremlin in time of civil disturbance or war.
The existence of "Metro 2", as it has become known, has long been rumoured. Officially, even in these post-Soviet times, it does not exist. Agents of the FSB, the successor to the KGB, called in one Russian journalist for questioning after he wrote about the secret network.
If Eugin's story is true, he is one of a very few outsiders to have been to Metro 2, and emerged with photographs to prove it.
They are images of huge tunnels, well-lit, a floor of concrete with rails set into it: ready for a train, a truck, or perhaps a tank. According to Eugin, the tunnels run for 25km, out into the countryside. He would not say how the diggers got in.
There are said to be around 100 diggers in Moscow. They are, on the one hand, extreme sportsmen and women seeking an adrenalin rush. But they are also uncovering the secret history of their city and their country as, on the streets above, smart boutiques and flashy cars are the new face of Moscow and of Russia.
The underground is an escape, too, from the pressures of a fast-changing society that is still in transition from the many decades of Communism. One woman said to me: "I feel at peace underground."
And there are stories of buried treasure. Some seek the lost library of Ivan the Terrible, priceless documents in a secret chamber, hidden for hundreds of years. I learn that this may or may not be a Russian fantasy.
"Go! Now! Quickly!" Back in the park, the manhole cover had been dragged aside. Several of the beer-drinkers looked up. Eugin was gesturing towards the dark hole.
Moscow's manhole covers hide a secret subterranean world
My dungarees more or less in place, I scrambled down, my feet just catching some rungs below the surface. There was the sound of water, ankle-deep as it turned out, and fast-running.
As I reached the bottom, the manhole cover above was pulled back into place as Eugin followed me down. Another digger was ahead of me, with a torch. I'd been told this was the Neglinka River, first diverted underground by Catherine the Great.
It felt like a large drain.
There was a bricked arch a foot or two above my head, wide enough to touch each side with my fingers, pipes coming into it from every direction, and a strange rumble from above as we walked on.
"Cars," said Eugin when asked.
"Why on earth do you do this?" I asked. He just shrugged.
We walked for a while. My heartbeat began to return to normal. I began to see the point. There is a strange beauty about being underground. A kind of serenity.
There was no doubt that we were alone, but for the water, and the smells coming from the pipes leading to our river.
Our little party turned at what the diggers called the "waterfall", a drop of several metres at a right-angled turn.
We walked back, upstream now, the water running fast towards us. A stop, and then up to another manhole cover, opened quickly to reveal the extraordinary sight of the sky, a dark almost-midnight Moscow sky.
I had been told you had to experience being underground to understand what being a digger means and why they do it. I'm not sure I would do it again, but I think I do now understand the appeal of this hidden underground world. And I certainly look at manhole covers in a very different way.
You can hear Diggers of the Underground on BBC Radio 4 on Wednesday 6 July at 1100 BST and for a week afterwards on BBC Radio 4's Listen Again page.