I think this is "Kwartier BPO – Sta Graven (Grez-Doiceau) (…. 2003 – 2017 ….)
Rue du Domaine en Rue du Bois des Fiefs 58, 1390 Grez-Doiceau" (from https://belgiummilitary.wordpress.com/diverse-2/belgian-pipeline-organisation-bpo/ ).  You can see the fencing with C3 (forbidden) signs "militair domein" from the N25.
I think fi.
https://www.openstreetmap.org/way/458966934 will probably be 'access=no'