Walkway

At Heathrow Terminal 5 most domestic and European flights go from the "A" gates in the main terminal, but long haul go from the B or C gates, which the vast majority of people access on a little underground shuttle train.  There is also a tunnel you can walk though though, and when I'm about to spend many hours on a plane the idea of a good walk tends to appeal to me.  It's only 750m but it's better than cramming into the transit.

I don't know whether people don't know about it, or just don't like it, but as seems to be the case most time's I use it, I was the only person there.