Tunnel vision: Hot, humid and noisy

The odor was a mixture of steam, petrol, mud and metal, mixed with something quite unidentifiable. And it was hot and humid.

It was also so noisy that I had to shout to be heard by the person standing just half a meter away. We were 15 m underground, near a tunnel-boring machine working to slowly lengthen Line 10 as part of its second phase, and part of Beijing's gigantic subway building project.

The new tunnel, 6 m in diameter, is nearly half a km long and is served by a railway track to ferry parts into it, and take the mud and debris out.