Start here before chasing ruins around town. The museum displays Buddha images, inscriptions, ceramics, and other finds from old Chiang Saen, with enough context to show why this quiet Mekong town mattered in Lanna history.
The building is small, so it will not swallow your day. Pair it with Wat Chedi Luang next door, then use what you have learned to read the half-buried chedis and brick foundations scattered through the old city.