South of Castel Nos, you will see the raised dome of what is clearly a hillfort, raised up above the river in a naturally strong position to defend. What is curious about this fort is that we have no historical record of its building, implying that it might be a Welsh effort in the medieval times to construct a motte-like fortress here in Maerdy Valley.

Across from the hillfort, you’ll see quite the opposite attraction. Delving deep beneath the earth in search of black gold is the site of Maerdy Colliery. Running for over 100 years from 1875 – 1990, the mine always maintained a reputation for left-wing political activism. In the 1926 General Strike, its militant stance led to the South Wales Miners Federation suspending the mineworkers' lodge and expelling them completely in 1930. The South Wales Daily News coined Maerdy the name “Little Moscow”. In a display of support, female workers in Moscow even sent a red Soviet banner in 1926, made for British miners and their wives.

The mine maintained its left-wing roots right through until the 1984/85 miners' strike, when no Maerdy miners would cross the picket line to work. The wives formed the first women's support groups in the South Wales Coalfield, organising food collection and distribution, and joining their husbands on the picket lines. Its eventual closure in December 1990 brought an end to a century long era of proud working-class socialism, and now it remains as an invisible warren of tunnels, hidden below the earth of the Welsh Valleys, black as the day it was delved.