I liked the cultural triangle and Yala national park.
From Amanwella you can take a leopard safari. In our original itinerary we were going to go to Amanwella and Galla, but instead decided to stay at Chena Huts and Ani Villas. In our old itinerary we had a trip to Yala national park scheduled. It's about a 2 hour drive in each direction but we absolutely loved the safari, and of course we stayed there. And according to the guide we had the best leopard sightings he's ever seen, so we did get lucky. Yala is a bit of a zoo, though, with lots of people....
The cultural triangle is possible if you catch a Cinnamon Air flight from Galla.