One of the exercises I often practice is actually in the tube, when I feel I've had a long and busy day. I like to meditate on sounds around me. Being in a noisy wagon is perfect. I mindfully hop from sound to sound: the sound of the train vibrations, the doors closing, people talking, the sound of newspapers ruffling, someone on the phone, foot steps, high heel taps, a scratch, entering a tunnel, two trains passing in opposite directions, the doors opening, people running for the train, people shuffling out, phone conversations, zippers, earphones booming...whoever thought one could find peace from thoughts in a noisy carriage? And then I've arrived at my destination with a clear mind.