Buried Tidegate of the Four Elements

A collapsed arch opens into ankle-deep black mud and brackish water before a circular stone door set into the ruin wall, its bronze seams furred with green corrosion and shell growth. Four sunken rings frame a central lock, each ring carrying a faint elemental motif that only catches the light when the water shivers. Every few breaths the door gives a low groan, and a pulse of trapped pressure bubbles through the mud from hidden vents, hinting that the mechanism is still alive beneath the ruin.