The quiet places follow a pattern in every country: the second-tier towns one region beyond the famous ones, the villages on the slow train line rather than the express route, and the coastal or hill settlements without a single postcard landmark. That absence of a headline sight is exactly what keeps them peaceful, and daily life there is the attraction.
Good hunting methods: look at where city dwellers in that country go for their own weekend breaks, which is usually charming but rarely internationally marketed; pick wine, farming, or fishing regions with scattered guesthouses rather than resort strips; and consider farm stays, rural homestays, or small family inns, which most countries have in some form.
Timing multiplies the quiet: famous-adjacent places are empty on weekdays and out of season. Use regional trains or a rental car, stay two or three nights rather than day-tripping, learn a few greeting phrases, and let a slow morning at a village cafe be the plan.