When Kev raised this idea for an incursion into the tube, I wasn't overly keen. It was going to involve over a kilometre of zero clearance tunnel to get to the target area. However the more I looked into it, the more it appealed. As a work of engineering, it's quite a feat. This illustration from 'The Eagle' in 1950 shows the layout. The crossover section features 6 tunnels, in pairs of 2. 2 of the tunnels swing around the outside, 2 come up the middle, and 2 dip under a tunnel before popping up at Camden. The tunnels are further broken up into 3 Southbound, and 3 Northbound tunnels. This involves a Southbound City branch tunnel, a Southbound Charing Cross branch tunnel, and a swap tunnel to allow a train to go from the City Branch to the Charing Cross branch if needed. The Northbound tunnels being the reverse of this layout.

When we originally did Euston Disused Station, the access route we used was so obvious, we were sure we'd be caught. Having used it 2 or 3 times, we were fairly blaze about it. As such, we tried it again, and it worked like a charm. It wasn't long before we were again climbing down the dusty grey vent. We climbed into the short access tunnel that leads out to the live Northbound track. The tunnel was eerily dark, and a traction indicator box glowed from across the way. The glowing emanated from the worryingly illuminated word 'ON.' If you're a trackworker on the London Underground, the map on the traction indicator box shows the easy to follow layout of the Camden Crossovers.

As we walked up to crossovers, we were pleased to see there recesses every 100 or so metres, so should a train come along, we would be alive after it's passing. Rather than spread down the tunnel walls. There were a couple of short dead-end tunnels leading off on the right as we approached the junction. It seemed a really long time before we finally saw a golden glow in the tunnel ahead. We'd walked about 1.2km next to live rails. Finally we walked into one of the first crossover sections.  On the illustrated map above, we'd walked up tunnel 22, and were tunnel 14 is on the right just behind the camera. The white light on the left is Camden Northbound Edgware branch. Kev pauses in the middle of the shot.

A closer shot of the above, taken with a prime lens. Kev had been investigating up the tunnel on the right which leads to the Northbound High Barnet branch. The shot below clearly shows the result of the 3 Northbound tunnels, the track from a tunnel on the far left is the swap track from the City branch, the left branch is the Charing Cross branch Northbound Edgware branch. And the track on the right with Kev striding across is the Charing Cross Northbound High Barnet (aka Highgate) branch.  It takes quite a bit of patience to be here, as one can see, there are lots of sections of live rail (with porcelain cups beneath), some quite short. Touch the wrong one, and it was game over.

Turning 180 degrees, the two Northbound tunnels are signposted with their intended destination. We had come up the City Line Northbound tunnel.

After snapping the Northbound section, we headed down the Highgate Northbound tunnel seen above on the left. We were looking for a way to get to the Southbound tunnels, which didn't materialise. Instead we found ourselves outside a station, this was Mornington Crescent.  The lit up bit of station and approach tracks on the left are the Southbound tunnels. The Northbound tracks head into the tunnel this shot was taken in.

Southbound platform of Mornington Crescent on the left, Northbound on the right. We could have walked up the Southbound tunnels to the crossover junction, but I hadn't felt comfortable the whole time I'd been here. So we opted to think about leaving.

Turning around from the above shot, the right hand tunnel is the one we walked down from Camden. You might just be able to see on the left hand tunnel, the gradient is dipping down. This is the swapover tunnel that dips below the others.

As we walked back down the Charing Cross Northbound tunnel, we spotted a small recess with a ladder leading down to what I think might have been the swap-over tunnel in the above shot. At this point the swap-over tunnel would have been much lower than the other tunnels.

We opted to walk straight out of the former station building when we finally got all the way back to the surface. I'd been rather worried about such a long distance with live rails, but as with pretty much all our incursions to the tube, it was fine. Thanks to Kevin Arnold.