A large enclosed underground octago...

A large enclosed underground octagonal chamber with no sky exposure. Thick dark cobblestone and polished slate walls with tall wooden support pillars and heavy wooden crossbeams across a flat ceiling with hanging lanterns. Flat stone floor with a slightly raised center platform. Four evenly spaced tunnel archway entrances (north, south, east, west), each framed with a stone arch and wooden trim. Dark, rustic, industrial aesthetic — like an underground mining outpost. No windows or roof openings.