NeverWet is a water-repellent spray that can basically keep anything dry. It's cool, if not the most practical thing in the world. But apply it to a pavement, let it rain, and magical things start to happen.
The project is the work of artist Peregrine Church, whose (entirely laudable) mission was to "make people's rainy a little bit better". To do that, he sprayed NeverWet through a stencil onto the pavement, making select parts of the promenade completely waterproof.
The result, as you can see above, is games and illustrations that appear when it starts raining: the dry bits of sidewalk carrying the message stands out from the wet. You've got everything from hopscotch to inspirational messages — basically, anything you can stencil onto a sidewalk.