Chironian fire pit. This temple is set within one of thousands of abandoned mine shafts where argillaceous limestone, or limestone with a high clay content, was dug out of the ground in the 19th and early 20th centuries. Baked and crushed into powder, it would reconstitute into something as strong as stone when mixed with water. Often called 'Rosendale cement', this material is practically indestructible, and has the property of being able to set under water. It was used to construct the foundations of the Brooklyn Bridge, the wings of the Capitol Building in Washington, DC (above which the House and Senate sit), and many other buildings that will be the last things left standing when the archeologists of the next age show up. Rosendale natural cement was replaced with a far inferior product created by the chemical industry, called Portland cement. More information on Rosendale natural cement at this link.