We had the opportunity to measure on the outer northeastern slopes of the Josefov Fortress. There are several underground corridors. One of them goes parallel to the fortification and from it branches perpendicularly turn to the foot of the slope. These were filled with gunpowder at the ends in the event of an attack on the fortress, and if the enemy army was moving over the place, the bomb was detonated.

The scale on the right applies to the depth in the rock, the scale on the left is for air reflections, we can use it to approximate the height of the cavities.

Here, the connecting corridor is captured when measuring up a slope.

Downstairs is a corridor for storing charges. The ceiling is about 4.5 m below the surface. A red area rises above the gallery, which contains more water. During the excavation of the gallery, the surrounding rock was broken and more water is concentrated in the cracks above the ceiling.

Here at the foot of the slope we found a large buried hole. It looks like a crater after an explosion, but the fortress never directly intervened in the fighting. Was it a test or was it an explosion by accident?

On the slope you can see long layers, which were probably filled. The original hill in the left part can be clearly recognized. At the top left is a gallery at a distance of 4 m, which leads inside the fortifications. It’s such a blue tooth, the signal is too strong and doesn’t draw the gallery completely. Below the gallery, only the resonances of the waves in the gallery above them can be seen in green.