This Cold War–era site contains a large radio telescope now run by an academic institute and used for astronomical studies. Hidden in the forest 24km north of Ventspils, the Irbene facility was used by the Soviets to spy on American satellites. Today, the huge 600-tonne, 32m-dish mounted on a 25m-tall concrete base is open at certain times for tours. To visit, call or email at least three days in advance to book a spot on a tour.
You can also stop by the building the tours depart from to see if they have any spots available on the day. Just driving into Irbene is an adventure as you pass by blocks of abandoned Soviet housing that look like Chernobyl.