The calculated distance (air line) between Burg auf Fehmarn and Oldenburg in Holstein is approximately 15 miles respectively 25 kilometers.
By car or train, the actual journey to Oldenburg in Holstein is certainly longer, as only the direct route (as the crow flies) between Burg auf Fehmarn and Oldenburg in Holstein has been calculated here.
Air line (approximately)
25 kilometers
13 nautical miles