this dream happened a lot during the 1980’s. It had several variants and seemed to evolve over time.
I am at a dug in gun emplacement. Initially it is just a gun emplacement, in a tunnel, that has been overrun. Years later I wonder why. I watch from inside the gun emplacement a hoard of trolls show up and overrun the gun emplacement. The gunners put up a fight, but they are no match. As an observer I escape trough a hole in the ground. One day, later, I wonder what is in the hole in the ground. There is an air-conditioning fan. It takes up all of the small duct. But there is a gap, I let my self past the gap. They do not seem to understand how I escaped down here. I do this several times.
A minor variant is that there is an underground river. On either side, there are gun emplacements. In both cases they are overrun. The gunners never win.