Bentota is where the west coast does the classic beach holiday properly: a long strip of sand, a calm river estuary behind it, and enough infrastructure that a family can be very comfortable indeed.
The river is the surprise. A boat through the mangroves at dawn turns up monitor lizards, kingfishers and mangrove crabs, and the estuary is a nursery for everything.
Lunuganga, the country estate of Geoffrey Bawa, is fifteen minutes away and is the single best introduction to Sri Lankan modernism anywhere.