Trincomalee
A deep-water bay on the northeast coast, and an overnight on the sacred-heritage route.
Trincomalee gets one night on the published pilgrimage route, between Dambulla and Jaffna, with dinner included on that night. The bay and the temples are the stop. It is also a candidate for a longer swim holiday in the months the northeast is calm, roughly May to September.
Do not pair it with a south-coast villa in the same short week. The island is wider than the map suggests, and this drive wants its own day.