I hate the people who came up with this one because I love this so much. I mean, I would love to have worked on this idea, what a fun project. It's all in the details too, the design of the sound-billboard where each little plug has a different sound, is terrific as well. The billboard installations are a little clumsy looking due to all the tech inside, but since they're a temporary installation that works anyway. at 22 seconds in, you'll be treated to the the exotic sound of Parisian sex.
To encourage people to use the train to go and explore nearby cities, Thalys created three interactive billboards. Each billboard represented a city, and each was host to more than 1000 unique sounds from that city. Pedestrians were invited to plug in with their personal headphones and start exploring.