During the Open Monumentendagen (Heritage Days, abbreviated in Dutch to OMD) you can visit one of the approximately 4.000 historical buildings and sites that open their doors to the public in the Netherlands. In Eindhoven you can for instance visit the the Dr. A.F. Philips observatory, complex Mariënhage, the Parktheater and the Van Abbe Museum. You can find the program for Eindhoven here: https://www.architectuurcentrumeindhoven.nl/agenda/, to see the program for the Netherlands here: https://www.openmonumentendag.nl