When I first saw pictures of this place emerge, I was very much taken with it. Seeing how the urban infrastructure works interests me greatly. The things we don't see that are either not known about or taken for granted. I'm still not 100% sure of their purpose, but I get the impression in times of traffic build-up in the tunnel, the fans suck the toxic air from the tunnel. Thus creating a vacuum to be filled by 'fresh' air.
This site was located and first explored by Danny Silentmotion, a driving force in London exploration. I found out it's location from Speed, who'd known about it for awhile, but never acted upon it. Getting in was a case of finding a door that opened, not too difficult. This is looking through one of the vent grills into the tunnel.

The long corridor that runs parallel to the tunnel road. The tunnel road is on the left here.

Probably the strangest element of the tunnels, round cylindrical tubes that go underneath the road. On the far side are the various fans.

A pipe ninja takes a rest in one of the tubes that runs under the road.

The other side of the tubes and some pipe ninja cloning going on.

"Well that's just crazy man." climbing up outside the safety cage to the main level.

In case you hadn't had enough pipe ninja tomfoolery, here's just a little bit more.

Looking down from what I'll call the main level to the tubes. The road would be through or just above the wall at the top of the picture.

The ventilation fans, three of them sit behind the camera in the above shot.

Walking back to the top of the ladder by the yellow painted steps above, I went through two heavy metal doors into the main room in the complex. Kev and Gringz stand above the door from the vent tubes area into the main room. A back up generator and various electrical gubbins in front of them.

Looking like some sort of ye olde street scene. Leading out past some more ventilation fans to a corridor that runs alongside the other road tunnel.

Turning 180 degrees from the previous shot, more fans the red door leads into the opposite end of the main room, mentioned above.

The business of ventilation, in the main room. You can see the heavy metal doors used through the complex here.

As Athlete sang, "You got wires." Probably a mixture of data wires and power supply.

Suck it and see. The main hall had six vent fan ensembles in, arranged in two groups of three. These are the three that exit into the area with the tubes under the road.

Gringz admiring the wires, it's all about the wires.

Backup generator and exhaust, next to the fuses and other electrical gubbins monitor type things.

A weird trip into the urban underbelly of London. Thanks to Silentmotion for showing the way, Speed for the location and Kev & Gringz for the company.