There are a lot of places to be curious about, so we started a Curiosity Travel Instagram. Where will your curiosity take you? Follow us!

The Calder Mercury Fountain may be the deadliest piece of art on Earth. The fountain, which pumps out pure liquid mercury, resides in the Barcelona modern art museum Fundació Joan Miró. You can visit it today—but don't worry, there is a thick pane of glass that protects viewers from breathing in fumes or, oh god, touching the lethal liquid.

Spain commissioned American sculptor Alexander Calder to create a monument to recognize the mines in Almadén, which once were the world's greatest source of mercury. (Not-so-fun fact: Most of the slave laborers and criminals working as miners died of mercury poisoning, because no one knew that was a thing yet.) Calder constructed a fountain in his signature style that pumped out mercury, not water. The finished piece was shown at the Spanish Republican Pavilion for the 1937 World's Fair in Paris, sitting in front of Pablo Picasso's seminal painting Guernica. That Picasso piece famously serves a political message in the context of the Spanish Civil War, and so does the mercury fountain. At the time, Almadén was controlled by Republican forces and under siege by fascist troops.

So back to the mercury. According to the World Health Organization, mercury is one of the top ten chemicals or groups of chemicals of major public health concern. This is something we've known about since 1866, but it didn't really enter the public's conscience until about the 1950s. According to the WHO, mercury exists in various forms: elemental (or metallic) and inorganic (to which people may be exposed through their occupation); and organic (to which people may be exposed through their diet). What's a healthy or normal amount of mercury? Zero. But now that we know mercury is toxic, we have ways to reverse mercury poisoning — as long as it's caught early.