OS Explorer Series (1:25,000 scale)
Map : OL12 Brecon Beacons National Park (Western Area)
The map shown below has good high level overview "road atlas style" mapping. However, it only zooms in to 1:50K OS Landranger mapping (with footpaths shown in red).
To view the more detailed 1:25K OS Explorer mapping (with footpaths in green), use the 'Bing 1:25K' link.