Just in case this site inspires anyone inexperienced in mountain walking to take to the hills, here are a few important notes:
1. You MUST have proper water-proof walking boots that your feet are comfortable in, and an outer water and windproof breathable jacket (Goretex or similar) and water proof overtrousers.
2. You MUST have a map (at least O. S.1:50,000) and compass and know how to use them.
3. Have enough food and water (with some to spare) for your planned hike.
4. Have an extra layer of clothing in a waterproof rucksack - the temperature and wind speed may be very different at 700 metres to in the valley. Gloves and a head covering of some sort are also essential in all but the summer months (when a sunhat may be necessary).
5. Although your mobile phone will probably work on the high ridges, it may not do so in the valleys. It is wise to tell someone where you are going and when you expect to be back.
Although the Black Mountains are not that high and rugged, they are still mountains and must be treated with respect. The Northern plain around Waun Fach, Pen y Manllywn and Ros Dirion in particular are rather featureless and best avoided in low cloud, even by experienced walkers.