Anglesey Coast path, a circular route of just over 125miles, that circumnavigates the entire island.
Stunning views, and possibly the most rewarding and leisurely long distance route in Wales.
There is nothing technical or demanding about this walk around the island, and if you want the best guide for the walk, get a copy of Walking the Isle of Anglesey Coastal Path by Carl Rogers.
No doubt other forum members will have their own personal favourite, but every time i have a go at a section of the path, i am amazed at what's on offer in such a small area of Wales.
The only hilly bit, if you can call it hilly, is the section from Bull Bay towards Wylffa Nuclear Power station, and as its the most northerly point in the whole of Wales, it has amazing views.