Open Monuments Day is held every year halfway through September, when thousands of monuments in the Netherlands are free to the public. The participating monuments can be recognized by the Open Monuments Day flag as shown here.
Open Monuments Day is organized to encourage people to know more about their historical surroundings and to encourage proper conservation of the monuments. During Open Monuments Day, thousands of historical buildings and locations (about 4,000) are open to the public for free. In addition to opening their doors, many locations also organize on-site activities such as exhibitions, music and guided tours.