Eryri is the busiest adventure country in Britain, and its operators are spread across its towns. Llanberis is the base for Yr Wyddfa and the lake. Betws-y-Coed and Capel Curig cover the eastern mountains and the forests. Blaenau Ffestiniog has turned its slate quarries into zip lines, mines and bike trails. Bala has the white water. Guided days on Yr Wyddfa, Tryfan and the Welsh 3000s are worth booking if you are not confident with a map in cloud, which is the usual weather.