The Meridian Lock

You enter a circular observatory buried beneath the ruins. Dust hangs motionless beneath a cracked dome, where a narrow shaft of daylight illuminates a bronze basin set into the floor. Eight glyphs ring the basin, their edges polished by countless hands. A stone door stands beyond it, covered in star-shaped holes that pulse with faint blue light. The air smells of old rain and hot metal. Whenever someone approaches the basin, the dial trembles and the nearest glyph gives a soft, distant chime.