A good starting point is to have a wander around the capital, Castries. Much of the town itself is very modern, as it had to be rebuilt after two fires. The oldest remaining part is the 'Hill of Good Luck', or the Morne Fortune Historic area, which offers the best views. You'll also find the 18th century, historic military buildings of Fort Charlotte here. Also worth a look, is the Cathedral of the Immaculate Conception, and Columbus Square, in the centre of town, with its lovely 19th century buildings. Castries also has a picturesque harbour area.
Head further south, and see the banana plantations at Cul de Sac. The oldest is the Marquis Plantation, where you can see the old slave quarters. Go further and you'll reach two of St Lucia's most amazing natural sights the dramatic Gros Piton and Petit Piton, two incredibly steep, twin peaks which tower majestically out of the sea.
The nearest town is Soufriere, St Lucia's oldest town, where you can see old Creole buildings. From here it's only a stone's throw to the world's only drive-through volcano. You'll find the Sulphur Springs Park at the centre, where you can take a therapeutic dip in the bubbling sulphurous waters. While you're here, see too the Diamond Falls, a volcanic waterfall, surrounded by amazing tropical gardens.
Other places of interest in the south, that offer a fascinating glimpse of St Lucian history, include the Fond Doux Estate, a cocoa plantation, where you can still see the original plantation house, and Morne Coubaril Estate, a working cocoa and coconut plantation. The Balenbouche Estate, now a working farm, is another historic place of note where the old plantation house is surrounded by an exquisite, tropical garden. There is also an old water mill and sugar mill.
Main attractions on the Atlantic side of the island include Errard Plantation, in Dennery, a restored fruit and cocoa plantation. Also, Visit Mamiku Gardens, fifteen acres of lovely gardens, set around an 18th century historic estate. Also, not to be missed is Fond D'Or Historical Park, a former estate, where you can see sugar mill relics, go hiking and relax on the gorgeous white sandy beach afterwards.