The Sanguine Weaver's Dial

The air in this cramped circular chamber is thick with the scent of coppery blood and burning sulfur. Centered in the room stands a massive stone pedestal with three concentric rings of obsidian that rotate with a heavy, grinding sound. Each ring is inlaid with crimson-glowing glyphs that pulse in time with a low, thrumming hum vibrating through the floorboards. Stains of dark, dried fluid trail from the pedestal down into narrow gutters that lead toward a massive iron door, which lacks any visible handle, keyhole, or hinges.