In Sweden, in the Greater Stockholm area, there are two completely different fortresses that are located on opposite sides of the sea fairway:
Fredriksborg Fortress = 59.40037, 18.44224 and
Oskar-Fredriksborg Fortress = 59.39861, 18.43563.
When you try to register the Fredrigsborg Fortress, your system returns the following message:
"duplicate record. A similar record to Fredriksborg Fortress already exists with 'Oskar-Fredriksborg Fortress' and id =12104321 in 0.3640166613051143 km distance".