After a long flight from Heathrow (or anywhere else for that matter), there's nothing better than an outdoor swim in a rooftop pool without even leaving the airport. If you have a few hours stopover in Singapore airport, follow the signs for the spa - it's a bit of a trek, but very much worth it. For about GBP8 you get a swim, a towel and a free cocktail by the pool. Generally very quiet and wonderfully relaxing. Even better if it rains!