The Swallowing Pool's Eye

The surface bowl above the Karth Deep where the river makes its last open turn before going black underground — a perfectly still meltwater eye ringed by Meltwarden warding-cairns and cold-blue witch-lights.

Stand here and you are directly above the thing the Meltwardens guard below. The pool is mirror-still even in wind, because the inflow and outflow cancel exactly. In fog it looks like a held breath. The Meltwardens say the stillness means the deep is watching back.