In South (the lower 1/3 of Trinidad), there are a few mud volcanoes. The largest and most popular of them is the Devil's Wood Yard.
These scaled-down volcanoes are constantly oozing and bubbling. While you may not actually be present for an eruption, evidence will show that they are constantly active.
Devil's Wood Yard got its name after the first eruption in 1852 shook the ground, knocked down all the trees and scared the villagers.
To get to Devil's Wood Yard, you will have to go ~10km east and slightly south of Princes Town. After you pass through Princes Town, there will be signs.
Entrance is free and there is no attendant.
There is a famous beach called 'Maracas beach' just outside Port of Spain. It is quite busy, but a must stop-off for a 'Shark 'n Bake' sandwich.
The gem I'm telling you about is a little further along called 'Las Cuevas Beach' - this is empty and has some great waves. You can pretty much get the beach to yourself.