Topoguide (in English) of the Snowdonia Slate Trail (England) edited by Rucksack Readers.
The guide is spiral, lightweight, waterproof, and includes a general map of the trek.

Description provided by the publisher:
The Snowdonia Slate Trail is a waymarked trail that runs for 83 miles from Bangor on the North Wales coast, making a circuit through the heart of Snowdonia to end at Bethesda. The trail joins up villages with a choice of welcoming accommodation. The walking is varied, ranging from easy valleys to mountain passes, from wild moorland to river gorges.
Highlights include the National Slate Museum of Wales, stunning views of Snowdon and nearby mountains, and abandoned slate villages high in the hills. The trail also passes the Penrhyn quarry with its impressive galleries of slate crossed by the longest, fastest zip-wire in Europe.
This guidebook is in rucksack-friendly format and printed on rainproof paper. Lavishly illustrated with 95 color photos, it contains large-scale mapping and all you need to plan and enjoy your holiday:

14 pages with clear mapping of the route at 1:40,000
practical information about public transport and travel
section with inside knowledge on how best to climb Snowdon
detailed route descriptions including where to find refreshments and accommodation
background on the slate industry heritage, the 'Great Little Trains of Wales' and wildlife.