The Monastery of the Holy Transfiguration of God is a colorful historical building with intriguing art, stories of good fortune, and tales of misfortune. It’s also surrounded by little mysteries—crumbling buildings, tumbling boulders, unsettling crypts, worn gravestones, foreboding artwork, and at least two tunnels. 

One of those mystery tunnels is located a few hundred meters downhill, on the winding road leading up to the monastery. The tunnel entrance is only visible to passersby in winter, when the leaves have fallen from the trees that mask its presence.

The unassuming steel door, concrete arch above it, and the regularity of construction indicate that this is a relatively modern tunnel, but none of the locals seem to be able to tell when or why it was built. Most likely it was constructed during the Cold War.

Park across the road (on the right if you’re going uphill), make your way through the underbrush to the entrance, pull open the great, green metal door, and the tunnel stretches away into the darkness.

Assuming you have a torch, it’s safe enough to venture all the way in until you meet the pile of rubble that blocks the tunnel, about 60 or 80 meters from the doorway. Until that point, the tunnel is solidly built and arrow straight. Where it leads to next is hard to guess. 

As you explore the tunnel, which has no side branches, notice the lack of graffiti, vandalism or damage (aside from the collapsed roof that blocks further exploration). It’s dry, quiet and peaceful; signs of a space that’s long gone unperturbed.

The only signs of previous human presence you may see are patches where small fires have been lit in the middle of the floor. Pages torn from what looks to be a collection of mechanical manuals fueled these fires. Their age indicates nothing in particular about the origins of the tunnel, as aged books are commonplace throughout Bulgaria.