Looks like a concrete cap placed over a toxic waste dump, e.g. Runit Island has one: https://upload.wikimedia.org/wikipedia/commons/e/ea/Runit_Dome_001.jpg htt

Looks like a concrete cap placed over a toxic waste dump, e.g. Runit Island has one: https://upload.wikimedia.org/wikipedia/commons/e/ea/Runit_Dome_001.jpg https://upload.wikimedia.org/wikipedia/commons/e/ea/Runit_Do...