Video made at the Antwerp, Belgium Train Station. . . with no warning a recording of Julie Andrews comes on the Public Address system. . . some 200 Dancers begin to appear from the crowd.
I've watched that video several times and really enjoyed it.
I did a little poking around to learn more about the dance. It turns out that this was a promotion for a reality show in Belgium where they picked an actress to play the part of Maria in The Sound of Music. (There was a similar show in England.)
Here's another video that tells about the making of the dancing video. Even if you can't understand the language (Flemish?), you will understand and appreciate what went into pulling off this dance in the station.