This is a photo of the Chernobyl "Elephant's Foot", a solid mass made of a little melted nuclear fuel mixed with lots and lots of concrete, sand, and core sealing material that the fuel had melted through. The photo was taken in 1996. At that point, the Elephant's Foot had cooled enough that a human being could stand directly in front of it for an hour before receiving a lethal dose of radiation. When the Foot was first discovered, shortly after the 1986 accident at the Chernobyl power plant, it delivered a lethal dose in just five minutes. You can read Kyle Hill's interesting history of the Elephant's Foot at Nautilus. And be sure to check out this 1991 video that shows how people were able to rig up robotic camera systems to safely take photos of the thing (though, as Hill points out, not all the photos of Elephant's Foot were taken safely).