Herr Strucker, it’s the Avengers.
HYDRA, led by Baron Strucker, is conducting their experiments with Loki’s Scepter out of an old Sokovian castle. The castle used for the exteriors is actually Fort Bard in Italy.
Int. HYDRA Research Facility
Before The Avengers can stop Strucker, he begins dumping all sorts of his data on the experiments that HYDRA was performing. The Great Tower and the tunnels underneath Dover Castle were used for the interiors of the HYDRA facility.
(Avengers: Age of Ultron, 2015)