Slow Art Day, which is April 27 this year. There's also a Tumblr with good photos. Two things I notice about the Tumblr immediately: they seem to really like fun and lighthearted art; they post often, averaging 60 per week. I'll follow it for a while and see what I think.
Unfortunately, it's time to follow another example of my favorite(ish) topic: art attacks. A woman wrote something with a marker pen onto Liberty Leading the People this week in France. The 28-year-old woman was immediately apprehended, and the "superficial" graffiti has already been removed. The woman was described as being possibly "unstable" and is being evaluated. It seems she scribbled "AE911" onto the painting, a reference to Architects and Engineers for 9/11 Truth.