Leeuwarden

If you want to release 1000 toy balloons or more in the red-marked area, you need to request permission from the local air traffic control at least five days before the event. 

See military AIP, part 3 AD, EHLW AD 2.2 'Aerodrome geographical and administrative data'.

Available daily between 07:00 and 17:00 (local time) for requests for special flights, activities, and events.