Watch towers ringed by barbed wire loom over an icy lane. This slave labour camp, Perm-36, buried in a vast tract of forest shrouded by snow, was where the Soviet Union brutalised countless numbers of its citizens.

Hundreds of thousands were executed, tortured, starved or frozen to death after being sent to toil in the Gulag, the system of remote prison camps.

Perm-36, 60 miles northeast of the city of Perm in the Urals, is now a “Gulag museum”. As the iron doors clanked shut behind me, I wondered what horrors I was about to behold.

Taking pride of place in the first exhibit was a photograph of men sitting on a log, fishing. Another showed cheerful-looking inmates felling trees.

According to the museum literature,