Inside tiny room underneath a countryside field where workers prepared for nuclear war

A small, easy-to-miss hatch in a Welsh field once served as the entrance to a crucial part of the UK’s Cold War effort.

The concrete entrance sits in a field near Abercrave in the Brecon Beacons and is easy to mistake for a manhole cover at first glance.

The structure lies at the end of a line of long-abandoned telegraph poles 200 yards north of Tanygarth, Wales Online reported.

Those curious enough to lift the rusted metal cover will find themselves looking down a 14-foot shaft that leads into inky blackness.

A climb down the precarious ladder leads to a small room that was once used as a Royal Observer Corps (ROC) nuclear monitoring post.

Here teams of volunteers would have spent long, hot hours from the height of the Cold War between the USSR and US in 1965 until 1991, two years after the Berlin Wall fell.

The long-silent and decaying rooms of the monitoring post would once have been full of equipment, strange dials, and the chatter of the volunteers communicating with other nearby stations.

The power and location of a nuclear blast, should a bomb have ever been aimed at UK soil by the USSR, would have been measured by the devices and relayed along the chain of command.

Over 1,500 of the stations were built across the UK.

Most of the observation stations were identical, although one non-standard monitoring post was built in a cellar at Windsor Castle.

Many were closed much earlier than the Abercrave post – which lasted until the early 90s – because of structural problems or flooding.

Although many of the instruments have long since been stolen, removed, or rotted away, the post would once have been fitted with a ground zero indicator comprised of four pinhole cameras to record the position of a nuclear detonation.

One of the shafts, which is still visible on the surface to this day, would have linked to a fixed survey meter, a type of Geiger counter used to measure radiation levels from a nuclear blast, which was fixed to the ceiling of the underground chamber.

Many of the ROC monitoring posts have long since been filled in with earth, flooded, or fallen into disrepair and it may not be long until the rest of these rare pieces of British history are lost forever.