Viazul  buses have a twice daily service from Havana stopping at Cienfuegos, and a daily service from Santiago de Cuba stopping at Holguin, Camagüey, and Sancti Spiritus. There is also a service to/from Varadero stopping at Santa Clara and Cienfuegos that is not listed on the Viazul website. It leaves Varadero at 7:30AM and returns from Trinidad at 2:25PM. You buy Viazul tickets from the air conditioned office right in front of where the buses park, not from the Astro or local bus counters.
Travel via taxi, specifically, unofficial taxis are a great cost effective way to travel to Trinidad as well. Typically only costing double the bus fare for two people, you'll get there in less than half the time, and in much greater comfort. When traveling with children, you might find this the preferred method of travel.
Trinidad has not been connected to the rest of Cuba by train since a hurricane destroyed an essential bridge in 1992. There is a local train running to the Valle de los Ingenios.
Street names may be difficult to find, although the town is very small. Once you wander around you can find every thing easily. The central part of the town is small enough to explore on foot.
The waterfalls just outside of the town in Topes de Collantes are beautiful. These are accessible either by car or by taking one of the day tours offered by Cubatur. (The local bus service to Topes de Collantes hasn't run in years.)
There is also salsa dancing in the square at night. Check out the colonial homes and furniture too, the houses are open and some of the antiquities are visible from the streets.
Walk around in the old colonial center.
Go to the beach on the Ancón peninsula, a 5-10 minute taxiride outside the city center. It is well within biking distance from Trinidad; there may also be a local bus running (check at the local bus counter at the bus terminal, located on the left as you enter before the Astro counter). The peninsula is one of the few places in Cuba where you can access a great beach without staying at a resort hotel. Make sure you have mosquito repellent, especially if you intend to stay on the beach in the evening.
There is a museum close to the cathedral near the Plaza Mayor in the old colonial center worth visiting. The museum itself is fairly standard but you can climb up a rickety wooden spiral staircase to a tower which has superb views across the whole town.
Also the market in the old colonial center which is nice to walk around and look at the handicrafts - drawn thread tableclothes and linens seem to be a speciality. The vendors are refreshingly laid back, you can look around and get virtually no hassle or pressure to buy.
Climb the hill behind the town to get a great view. To get there, continue up the hill northeast from the Plaza Mayor.
Take one of the day tours offered by Cubatur. These include several options to Topes de Collantes, or a trip to the Valle de Los Ingenios on an old train with a restored carriage (if the steam engine is working ... if not, check back the next day). The train costs $10CUC per person. It is a nice way to spend a day for those with difficulties walking. The smoke from the steam engine can be thick, so watch out if you already have breathing difficulties.
Before you go:
There is a pizzeria, which is refreshing due to the lack of variety of vegetarian food in Trinidad. There are many other amazing places to eat with much fish and chicken cooked in imaginative ways.
Many casa particulares offer dinner, for a fee, which are usually authentic dishes and very well prepared and well worth checking out.
There are quite a few Paladars in the town, which offer quality home cooked style food which is usually served at the back of the hosts Casa or House. Its quite hard to find Paladars if you havent first been taken there by a tout or you have friends that could recommend one. If taken to a Paladar by a tout, be prepared to have their commission added to the bill.
There are several 'so called' peso pizza establishments in the town which allow tourists to purchase Pizza for the national peso price. This usually works out at around 5-10 national pesos or 10c. This is a good idea for travellers on a budget. One of the biggest places in Trinidad is situated on the corner of Frank Pais and Francisco Javier.
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.
There is a beautiful colonial hotel on the main causeway up to the square. It is a little expensive, but worth it as it has colonial rocking chairs and 2 four poster beds.
There are many casa particulares in Trinidad. It is an excellent way to meet the people of Trinidad and see how many live.