Hexengrund
About five kilometers north of Gdynia at Babie Doly (german Hexengrund), the Germans began in 1940 to build a test and research center for torpedoes. These were not U-boat torpedoes, but torpedoes suited for torpedo boats and aircrafts. Before that, germans had to buy torpedoes from Italy who technolgical were ahead of Germany in that area. The test facility itself was set up in a bay with calm water and at a safe distance from enemy aircraft, for the time being. Nearby there was also a commenced Polish air base completed by the German Air Force. A railway was built to transport torpedoes from the test facility to the air base. Other buildings were constructed for various purposes. From 1942 intensive tests were conducted on a torpedo called F5B, also suited for aircraft. In the final stages of the war, the test facility was conquered by the Soviet Red army.
Current status: Demolished (2021).
Location: 54°35' 08.59" N 18°32' 16.31" E
Get there: Car.
Follow up in books: Killen, John: The Luftwaffe: A History (2013).
About 400 meters from the beach in the middle of the bay is a huge stripped-down concrete block reminiscent which looks like an abandoned base from a Star Wars movie. This was part of the test facility. If one is allowed to visit the construction I don’t know, but probably not. It might be protected as a nature conservation object or something else. Closer to the beach there are remnants of piers and on land there are various concrete blocks and buildings that probably were part of the test facility.