Tide-Heart Combination Lock

The cavern breathes cool, wet air through a narrow chamber of black stone and pale calcite, its walls veined with glimmering mineral lines like frozen lightning. Set into the far wall is a circular lock of four rotating rings, each ring etched with symbols that catch lamplight in dull silver. Beside it, a bronze basin slowly ticks with trapped water, and a shallow drain channel runs along the floor. When the rings are turned correctly, the stone answers with a low rumble and a pulse of cold mist from the seams; wrong turns make the basin shiver and the floor grate with a warning click.