The Elephant’s Foot is the nickname given to a large mass of corium and other materials formed underneath the Chernobyl Nuclear Power Plant, near Pripyat, Ukraine, during the Chernobyl disaster of April 1986. It remains an extremely radioactive object; however, its danger has decreased over time due to the decay of its radioactive components.
The AZ-5 kill-switch button (top row in the middle) for the RBMK graphite-moderated nuclear power reactor, a security device intended for an emergency shutdown, SCRAM, of the reactor core.
The pressing of this button on the 26th of April 1986 at 01:23:40, would be the starting point of the Chernobyl Disaster.