There are multiple of these concrete oil tanks of the Kriegsmarine in the area of the former KZ Farge concentration camp. The bunkers were constructed between 1939 and 1941 and were meant to store the Kriegsmarine heavy oil reserve at the start of World War Two, but after the victory over France and the Low Countries, the reserves strorage demand shifted towards the Atlantic coast and the bunkers were unused for this purpose.
KZ Farge and U-Boot Bunker Valentin
When the Kriegsmarine started its ambitious project to build the massive Valentin U-Boat bunker in 1943, a satellite camp of KZ Neuengamme named KZ Farge was set up to house forced laborers. One of these bunkers was used to accommodate a large number of the estimated 3,000 men. Although this is not the actual Oil Tank Bunker (Ger: Ölbunker) where the prisoners of KZ Farge were put up, it does give a good view of the scale of this bunker type. The round bunker has a diameter of 50 meters and a height of 7 meters. The location of the original concentration camp bunker, 150 m southwest of here, is now marked by a commemorative stele.
Right after the War the oil bunkers were blown up by the British and rendered useless.
You can visit this site on the Neuenkirchen Heide in Bremen-Farge. It is located on active training grounds of the German Army, so access is only allowed during the weekends and public holidays.
In the area around this information point you can find many concrete remains of bunkers and barracks.