If you are going through the North Wales & Chester area the LLangollen canal, especially the Pontcysyllte Aqueduct, is worth a visit. That part of the canal towpath is officially a cycle route with quite a reasonable surface. The descent of the Horsehoe Pass into Langollen is fun!
For route planning, cycle.travel is good for finding quiet routes as it takes traffic levels into account. (Although it can be a pain if you DO want to follow a section of main road for a particular reason - if the routing algorithm takes a dislike to a road it will sometimes have you making a right turn onto a back road then another right turn back onto the main road a few hundred yards later, if there isn't an alternative, & then repeating the whole thing another few hundred yards further on! At least you can add via points, sometimes at 100 yard intervals, to generally persuade it to go the way you want.
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