The reduit of Fort bij Vechten (Fortress near Vechten).
The reduit is essentially a fortress whitin a fortress. If the fortress was fallen, the soldiers could return to the reduit and defent them selfs from the invaders till help arrived. It had it own supplies and defence system.
Fort bij Vechten was build durning 1869 and was used to defend the Houtense vlakte (Houtense plain). This because the plain is above sea level and unable to be put under water, what was a key element in Dutch defense in those day's. It's the biggest fortresses in Holland, together with Fortress Renauwen, they are the same size.
The fortress was manned by about 600 man.
Today the fotress is used as an information center about the Dutch defence line, and it's used for party's.