So out in the Pacific Northwest there are the remains of the US Coastal Defense
Forts Casey, Worden,
Columbia,
Worden
All of which might be repurposed for use during the Twilight War.
Similarly, I haven't see anyone mention the numerous
Flaktrum's that are in Austria and Germany. All of which unless they were ground zero probably still exist and may have been repurposed during the Twilight War.
As well I know in a numerous locations out west in the US there are block houses made out of wooden or stone (depending on your region). These usually had stocks of arms, powder, bullets, and food for folks to retreat to and defense themselves from hostiles in the region. One would assume that these would see a revival in a number of towns both in the US and Europe to defense against marauders. Granted these might not stand up against heavy arms like mortars or armored vehicles. That said, they still might be valuable to some locations as places to hide out and run off to when marauders come into town.