We did an independent tour through Cosol St. Lucia Tours
. It was a full day, but we stopped by a banana plantation, a drive-in volcano, a waterfall/botanical gardens, we got to snorkel at a site in between the Piton Mts, and we got fed lots and lots of yummy food. There were a couple other stops for shopping/views/snacks, etc. The staff was VERY knowledgable and friendly, and I would highly recommend it!