Bayahibe is the starting point to go to visit Isla Saona. From here sails the motorboats which every day get at the paradisiac island into the Parque Nacional del Este.
The huge Basilica de Nuestra Señora de Altagracia in Higüey (about 40 km from Bayahibe) has a real modern, strangely engineered look. An ambitious project, really impressive.
Walking through any of the jungle-forests that cover most of the DR, you'll see many colourful butterflies around. I am not an expert, but I saw so many different ones...
Saona - beautiful island, great beaches, not too many people - and Piscina Natural - great place for snorkeling - get away from the hotel crowd!
Go diving. There are beautiful places in the area around Bayahibe and there are a lot of small businesses that offer boat trips and also courses in diving.