Cicerone - Guide de randonnée à vélo (en anglais) - Cycling Lon Las Cymru (Pays de Galles) - 250 miles through the heart of Wales on traffic-free paths and quiet roads

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Guidebook to cycling Lôn Las Cymru, a 255 mile (410km) route from Cardiff, or 242 miles (390km) from Chepstow to Holyhead, showcasing Wales' beautiful rural heartland. Cycling is on quiet roads and traffic-free paths, and although there are some mountainous sections, gradients are mostly gentle. The route can be completed in 4 to 7 days.

Seasons
The best time to go is between April and October when the days are longer and the weather is at its best.
Centres
The route passes through many of the main towns in the Brecon Beacons, Black Mountains, Cambrian Mountains and Snowdonia National Park.
Difficulty
The route can be ridden as a leisure ride or as a challenge and there are schedules for both types of rider. There are mountainous sections in Mid Wales but gradients are never severe and some, such as that up the Vale of Ewyas, barely perceptible until the very top.
Must See
Lôn Las Cymru runs from Cardiff or Chepstow to Holyhead, passing through the heart of Wales. Translating loosely as Wales' Green Lane, it is the preeminent cycle route in Wales, passing through lush countryside, and following quiet lanes and former railway lines.

A guidebook to cycling the Lon Las Cymru cycle route from either Cardiff or Chepstow to Holyhead. Covering 410km (255 miles), this long-distance cycle through the heart of Wales takes 5 days and is suitable for both first-time and experienced long-distance cyclists.

1:200,000 maps and profiles included for each stage
GPX files available to download
Refreshment and accommodation information given for each stage
Suitable for all bikes 
Information on cycle shops along the route

(Source : Cicerone)