Covering 630 hills, from 500m lumps right up to Yr Wyddfa (Snowdon), the Welsh Highlands - Uchafion Cymru is a hill list on a grand scale. Myrddyn Phillips co-authors the list, and is also the first to complete it, a task that took nearly 20 years. What's the attraction of a bagging job this epic? Allow Myrddyn to explain...