Entering theaters at a timely moment, “The Cave” is a frightening immersion in life under siege in Syria that, as difficult as it often is to watch, can’t come close to replicating how harrowing it must have been to film.

The setting of the documentary, from the Syrian-born director Feras Fayyad (“Last Men in Aleppo”), is a subterranean hospital on the outskirts of Damascus connected to the world outside by tunnels and basement shelters. (With the site difficult to reach, Fayyad directed remotely for much of the shoot, relying on three cinematographers.)