If you want the relevant OS map for Trefriw and the area covered in our walks, the one you need is Explorer (OL) 17 (1:25,000 scale).
(Statistically you’re likely to have a copy already – this is the Ordnance Survey’s top-selling map!)
On one side is the Conwy Valley, with Trefriw sitting fairly centrally in it; all our walks lie on this side of the map. The other side is dominated by the Snowdon massif.
If the 1:50,000 is what you want, we’re on the very edge of Landranger 115.