Flakfortet, meaning sand-shoal fortress, is a sea fort located on the artificially built island of Saltholmrev, in the Øresund between Copenhagen and Saltholm.

Flakfortet was the last of three artificial islands that the Danes created to defend the entrance to Copenhagen's harbor.

Construction of the artificial island required the use of caissons of reinforced concrete, possibly the first use of such structures.

However, this fort required extensive renovation so in the interim (1965-1968), the Danes temporarily placed the HAWK battery on Flakfortet.

In 1975, the Danish Ministry of Defence leased Flakfortet to the Copenhagen Sailing Association and opened the site to the public.

It was put up for sale in 1999 under the guidance of Statens Ejendomssalg (commonly known as Freja), which is the department under the Danish Ministry of Finance responsible for selling surplus state-owned property.