I remembered seeing this post months ago and took a note for our trip to St. Lucia. We just returned. We stayed in a resort near Soufriere during our stay and used a hired drive to take us there and back. We only visited that one part of the island, but everyone we met said that it was the best - Ha ha! The roads are fine, but driving is on the left hand side and the roads are seriously curvy. Local drivers drive fast.
We toured what is billed as the world's only drive in volcano and saw all of the bubbling mud and ruins of an 18th century french bath complex. Guides take you around and they work on tips. You can do a mud bath there, but we passed. Also, Diamond Falls and gardens, where there are active baths where you can sit in the warm water, again with guides who work for tips. Try the Piton beer if you like beer. I don't love beer, but thought it was pretty good. There is good snorkeling right from the beach at Anse Chastenet and a lot of the snorkel tours bring people there. We saw an abundance of fish and some sea turtles.
The next door beach, Anse Mamin, has a gate leading back to the ruins of an old sugar cane processing plantation. A tour there was very informative.
We met others who got up at 5am to hike Gros Piton. It took them 4.5 hours round trip and they said their legs were wiped out. You hire a guide to take you, and it's strenuous but not technical. They recommended hing at least one hiking pole for getting back down. Going to the top of the Petit Piton is a more technical climb with ropes.
Water taxis are around in Soufriere if you want to hire someone to take you to the beaches I mentioned, or sugar beach.
When you he to fly out, know that upstairs at the airport there is a pretty good food court with lots of selection. Since there was no food served on our 5 hour flights in either direction, it was good to get some lunch before we boarded. And the airport is very small. You walk out onto the tarmac and down quite a ways before climbing the steps to your plane. I am not sure what the accommodations for disabled trelers are. An advantage was that we boarded by doors in both the front and the rear of the plane.
He a great trip!