Kosgoda is a turtle town. The main draw is the conservation project where you can watch hatchlings scramble to the sea. It's a genuine experience, not a tourist trap.
The beach is a mixed bag—expect rubbish in spots, but also long empty stretches. Most guesthouses are family-run, with pools that guests love and hosts who cook on request. Don't come for nightlife or restaurants; come to switch off.
Book a guesthouse with a pool—the sea isn't always swimmable. Rent a scooter to explore nearby Balapitiya and Ambalangoda. Two nights is enough unless you're nesting like a turtle.