The „Deutsche Gesellschaft für Festungsforschung“ (German association for fortification research)

 https://festungsforschung.de/kontakt/

What is the DGF? The „Deutsche Gesellschaft für Festungsforschung“ (German association for fortification research) was set up in 1981 and is a non-profit association, promoting the scientific research of fortresses and the practical translation of won perceptions in the range of presentation and documentation plus in the safeguard of the cultural and environmental heritage and landscape protection. Their members are historians, geographers, architects, engineers, town planners, museum experts, teachers, local politicians, committed citizens. 

http://www.internationalfortresscouncil.org/organizations.html