I was reading an interview with Will Self where he was talking about the pioneering pastime of walking from airports to the city centre rather than by the traditional conformant method of cars, buses or trains. Apparently he has done 4 such walks so far, plus a walk from Central London to Heathrow. He quite rightly pointed out that when he was doing the Heathrow walk, he had the thought that he may well have been the first person ever to do such a thing and in that respect he felt like more of a pioneer than he would have had he paddled down the Amazon. That was a nice thought.
He also mentioned that a sign on the tunnel leading to Heathrow stated, "No Pedestrian Access Please Return to the Renaissance". The Renaissance being a nearby hotel where the shuttle bus collects.