We've seen this place a couple of times before. It's at the town of Klevan, in the Ukraine, it has railroad tracks
going through it, and pretty squared off, presumably for trains. It's rumored to come from cold war secrecy
moving materials.
It's become a tourist attraction for whatever tourists make to the Ukraine boondocks, a local lovers lane, and
fuel for internet speculation and tall tales.
I've come to satiate your intense curiosity. The tunnel straddles part of a 7km spur from the main line to the
very busy Odek plywood factory, in the village of Orzhiv. The factory is humming 24/7 making Birch plywood,
which is stuffed into shipping containers, then loaded onto flatcars to haul out to the main line. They're making
so much plywood for western Europe sometimes their locomotives are making several trips a day through the tunnel.
You can see how the shipping containers square off the tunnel.
Now you know.
Pssst... there is a spur to a military base in the tunnel.
link