Editor's note: Following a jailbreak in Afghanistan when hundreds of Taliban prisoners tunneled their way out of Kandahar's biggest prison, CNN correspondent Nick Paton Walsh visited the scene for this exclusive report, from inside the tunnel.
Kandahar, Afghanistan (CNN) -- Once the furor died down after the jailbreak was discovered, it was the Americans' and Afghans' turn to start digging. The only way to find the tunnel that had led at least 475 Taliban to freedom was to burrow down a trench inside the jail courtyard along the length of the outside wall.
The tunnel began with a small hole in a cell in the "political wing" at Kandahar's Sarposa jail and ended at a house near the jail.
It was well-built and went at least two meters underground, from what we could determine. Support struts lined its length. A strong rubber ventilation tube lay along the bottom. Hooks stuck out from the wall, presumably to let the excavators hang lights. The men would have only had room to crawl through it, one by one.
There were small plastic wheels outside the trench, part of their trolley system, one American told me. The Americans I saw here were military police or U.S. Army.
The Taliban's epic escape -- the root of a "disaster" for the Afghan government, according to its own spokesman -- at first seemed too remarkable to believe. But after about 90 minutes of closely looking over the site, what seemed even more remarkable is that nobody had managed to stop them.
We arrived at the jail with the letter from the Minister of Justice that he had handwritten and signed, together with a seal of the Afghan prisons department.
But that wasn't enough. We also needed the permission of the Kandahar governor. Lacking that, we called Ahmed Wali Karzai, the president's brother and head of the local council, and also put in a call to the local governor's spokesman. Eventually, we were allowed in.
First we came across two young American servicemen who also were surprised at the scale of what had happened.
As is the customary parlance now among NATO, they told us this was an Afghan operation and they were simply there in reasonably large numbers to "backfill." That's what NATO says when it really means the Afghans have left a mess behind that needs a very large American mop.
While we were in the jail courtyard, three Americans in civilian clothes walked up and began measuring the tunnel's depth. They did not want to be filmed.
We then headed into the main jail building. To the west, lay the criminal block - still occupied, a little cleaner. To the east, where the Taliban were kept.
The corridor that once housed the Taliban was absolutely barren. Where days earlier agency pictures had shown blankets and litter strewn everywhere, now there were clean spaces. Cells had been stripped bare and locked again, except one room where the tunnel started.
Inside, the rudiments of daily life remained: blankets, jugs, and a heap of razor wire introduced by the Americans to ensure nobody would try to come back up the tunnel again and surprise them.
We filmed. Some of the Americans were concerned the several dozen escaped prisoners who have since been recaptured might be put back in the same cells.
And then suddenly the hospitality evaporated.
It began with the Americans, who got a call on their radio. Despite their repeated assurances this was an Afghan area under Afghan control, they intervened and said it was time for us to leave, immediately.
We tried to explain to the Americans that they were contravening the letter of introduction we had from the Afghan minister of justice, but to no avail. They did later ring to say we would be permitted to return the jail. But because we were so noticeable as a group of foreigners, we decided against going back to the same place twice in the same day because of the risk.
By that time, the Afghans had decided we should go.
We left, a little bemused, still wondering about the precise location of the house where the tunnel emerged.
However, a local policeman helpfully pointed to a house -- just across the road.
We crossed over and into the house's courtyard, and then its first room. There we found a hole, recently filled in, and guarded by six Afghan policemen, four of whom showed signs of being awake.
We began to ask ourselves how the escaped prisoners had then fled the house. There was a back door to the compound, but that led to a canal, over some rubble, and did not provide the clear access for the minibuses the government says some of them were whisked away in.
The easiest way out was the front door, as it led to the main, neatly asphalted road. This means the prisoners had crawled out of the tunnel and then most likely caught a bus right outside the prison's front gates.
But there was further astonishment to come. We had always wondered why the Taliban bothered to do this, particularly as their huge and complex tunnel took them only a few meters outside the compound? Why didn't they use a truck bomb to blow a hole in the walls as they had done at the same jail in 2008?
A discreet communications radio mast held the answer. Just a few feet down the road is a sizeable American military base -- presumably a response to the past escapes at the jail -- that seems to adjoin the prison.
The Taliban obviously had to be subtle in their approach; otherwise they would risk an American intervention and all the uncompromising firepower that entails.
So instead, they dug their way out, but under the noses of both the Afghans and NATO, emerging into the street to drive away a little more than 100 feet from an American military unit.