Black Mountain South Top is a 637.4m subsidiary peak of the Black Mountain just North of it and is classed as an hill. It is a fairly gentle bump on the landscape with a fairly flat top marked by a small pile of stones.
The walk to it, heading South from the Black Mountain, is interesting because it follows the Offa’s Dyke path and has multiple large stone cairns as well as some interesting sandy landscape parts. On a day with better light I imagine this is a very photogenic stretch of the walk.
The summit is marked by a small pile of rocks just off of the main path. There is nothing much else to see apart from the normal purple heather patches and bits of longer grass. Views are probably decent on a nice day, but it was really quite grey and foggy when I reached it.
An interesting section of the walk and a nice easy hill to tick off with gentle ascent and descent.