A Spanish bunker from the time of World War II next to the Guadiaro River, in Cádiz

After the start of World War II, Spain was threatened by the possibility of being invaded by both sides.

P Line, the Spanish bunkers built during World War II in Sierra Cavallera, Gerona
The old defenses of Fuerteventura: the batteries of Corralejo and Matas Blancas

In order to prevent a German or Allied invasion, the regime of Francisco Franco planned the construction of a network of fortifications consisting of more than 500 bunkers in the vicinity of the Strait of Gibraltar. This defensive network, popularly known as the "Strait Wall," was built by sappers from the 4th Fortifications Regiment of the Spanish Army, along with civilian workers and between 10,000 and 15,000 Republican prisoners from the then very recent Spanish Civil War, according to the San Roque City Council.

Yesterday, the excellent YouTube channel Aventuras Entresierras (which I recommend you subscribe to) published an interesting video visiting one of the bunkers of that defensive network, specifically a machine gun position built at the confluence of the Guadiario and Hozgarganta rivers, in the province of Cádiz, in order to defend a nearby bridge (the video is in Spanish, you can activate the automatic English subtitles in the bottom bar of the player):

You can see some screenshots from this video here. Here we see the Hozgarganta River suspension bridge, on the way to the bunker. It's in the municipality of San Martín del Tesorillo (Cádiz).

Here we see the machine gun bunker. We see the fighting chamber on the left and the access tunnel on the right.

The second part of the video includes an analysis of these two survival kits inside the bunker. The one I liked best is the one on the right, which says "Да Жит Испания" (Long live Spain) in Russian Cyrillic.