A large monitoring station used to gather important scientific data in the Baltic Sea has mysteriously vanished.

The underwater observatory, which had been on the seafloor since December 2016, is managed by the GEOMAR Helmholtz Center for Ocean Research Kiel and the Helmholtz Center Geesthacht (HZG). On August 21 at 8:15 p.m. local time, transmissions from the €300,000 ($330,000) station came to a sudden halt. Divers were dispatched to the site, only to find—much to their astonishment—that the entire structure was gone, save for a shredded transmission cable, according to a GEOMAR statement.