Location from pokemon-journeys by
The ruin beneath Galar where Eternatus was sealed -- a subterranean chamber that cracks open when Chairman Rose wakes the infinity-energy Pokémon centuries early.
The Darkest Day site smells like old dust and ozone. Standing in it for longer than a few minutes produces a low, continuous headache as the sealed Dynamax energy begins pressing on the mind. Before Rose breaks it open, the chamber is almost meditative -- the kind of ruin a scholar like Sonia would spend years mapping. After, it becomes a wound in the landscape, light leaking upward into Wyndon's sky, Eternatus unspooling out of it. It is both a historical monument and a doomsday clock. The site records the original Darkest Day, the two heroes (who later become Zacian and Zamazenta), and the sealing -- but it does not record how long the seal will hold without maintenance. Rose's mistake was assuming the math would still work. Ash, Goh, and Leon's job in the crisis is to hold the line long enough for the old heroes to wake up.
A vast cathedral-scale underground chamber of cracked ancient stone, with a raised central dais carved with two hero-silhouettes and a ring of runic pillars surrounding a sealed crystal pit. Dim red light pulses from the pit. Stalactites hang from an unseen ceiling. A wide spiral ramp descends into the chamber from a hidden entrance beneath Hammerlocke Castle.