Visit Castries market.
Visit Soufriere
The Black diamond falls has a garden and water fall. This is where a scene in "Superman" was filmed.
The drive through volcano is a great sight. There is a sulfur mud bath that is good for the skin. View the hot bubbling sulfur mud pits.
Experience the best view in Saint Lucia from the Ladera hotel. Stop in for a drink or grab a bite at the restaurant.
The Mineral Springs - just south of Soufriere, these hot springs are one of the main attractions on the island. There is a pool that the hot water runs through, so make sure to take your swimming trunks and go for a dip!
Take a sail boat ride down to the Pitons. Snorkel along the way. (http://www.sailsaintlucia.com/)
Find a private beach by asking the locals for a good beach to go to. Be prepared to walk down a winding road.
Stop on the side of the road and take pictures of the fantastic view.