https://ancienthistoryx.com/hierapolis-ploutonion-deadly-co2-gate-to-hell/
Hierapolis Ploutonion: The Deadly CO₂ “Gate” - Ancient History X
Jan 7, 2026 - Geogenic CO2 at Hierapolis’s Ploutonion reaches lethal levels, explaining ancient underworld rituals through modern measurements, geology..
ancient historyhierapolisploutoniondeadly