Placencia is a peninsula about 14 miles long..maybe longer.
Placencia village is at the southern tip of the peninsula.
Catdance62 listed some great tours and adventures

We have done many of them and some more than once.
Great place and totally different than Ambergris Caye.
The real Belize is mainland. Belizeans vacation on Ambergris Caye at holiday time
Use your eyes, you will see so much more on the mainland. Bring a book for down time. Enjoy!