The Museu Cerdà occupies the former Sant Domènec monastery cloister and tells the long story of the Cerdanya valley — from prehistoric and Roman remains found locally, through medieval town life, to the late-nineteenth-century summer resort culture that built the lake mansions. The museum is small and easily seen in an hour, with good explanatory labels in Catalan, Spanish, and partial English.
The highlights are the medieval altarpieces rescued from rural Cerdanya churches, and a careful section on the Civil War in the valley — the destruction of Santa Maria, the refugee crossings into France, and the bombing of nearby Puigcerdà. Free admission on the first Sunday of each month.