The best thing about traveling is that some experiences just crop up spontaneously.
Take a recent Saturday evening in Kiev, the capital of Ukraine.
It's chilly, and people hurry past on their way to clubs and restaurants, their coat collars turned up against the wind.
Young women clatter up the steps from the Teatralna metro station, oblivious to the sound that wafts up behind them — the sound of people singing.
The steps down to the metro station, one level from the street, lead into a big open space.