In the square at night, there are often events and there is a very good club open until the early hours. It is a lovely town with amazing visitors and inhabitants, and small enough for you to wander and choose your drinking hole. The Mojito's and rum cocktails are great.
There are also places where the locals hang-out and which serve quite decent beer at a very reasonable price. These places usually serve draught beer and stay open just as long as there is beer to serve. When the beer from one place has been drunk, then it's off to the next place or not. Many of the locals drink their beer outside on the street and Trinidad is so small so these places are easy to spot.