We took one of these tours, and visited three sites. First was a place called Tek Paul. (pronounced "Tea") This was a 45 minute hike through forest and farm, and is famous for its views. At various places along the trail you can see the valley of Chateaubelair, both Gros Piton and Petit Piton (the famous Lucian mountains, and a world heritage site), and the village of Soufriere. We really liked the views, and it was great to stretch our legs after a few days on the boat.
Next we visited a volcano. This is the only place in the Caribbean where you can drive into an active volcano caldera. 39,000 years ago there was a big eruption here, and the magma is still close to the surface. You see lots of mist, from rain water contacting hot rock. Pools of water are literally boiling, but look black and viscous from the suspended iron sulfide. The rocks in the area are stained with sulfur, copper, and iron. We are told that there are actual geysers, but only at the time of the full moon.
Finally we visited a very pleasant botanical garden. This was built by a father and daughter who owned the property and surrounding plantation. There are many, many beautiful tropical flowers, along with examples of the typical Caribbean fruits -- mangos, cashews, nutmeg, soursop, citrus, pineapple, coffee, and cacao. A feature of the garden is the unusual Diamond Falls. The water in this waterfall is the run-off from the volcanic caldera we visited. It is hot, and black, just like at the volcano. The rock under the falling water is brown with sulfur deposits. For a few dollars, you can soak in a pool with water from the stream (thankfully not black!). We hadn't brought our bathing suits, and skipped it this trip.