We booked all our Viazul bus trips on the viazul.com website before leaving Europe. My daughter is 11 and therefore entitled to a child fare. It seems the website incorrectly calculates the child fare - apparently there is a minimum. We discovered this when we arrived at Trinidad bus station. I offered to pay the difference (2 CUC's) but the very rude guy in the ticket office insisted I pay for all of us again and then seek reimbursement from viazul. I didn't have a lot of choice. Of course, I have had no response at all from viazul with my request for a refund. We had the same issue in two further cities but the problem was sorted out with a little "donation" to the ticket clerk. I am also convinced that viazul don't anticipate that people have booked on the internet. On the three buses we took, all were overbooked by roughly the number of people who had booked on line. The buses are fine but I wouldn't recommend to book on line. Just go to the ticket office in good time and pay cash. It's much easier.
From Cienfuegos we came to Trinidad by viazul bus.
There are two main bus companies in Cuba Viazul and Astro, the second one is the cheaper and mainly used by locals, Viazul is more expensive and practically created for tourists.The trip was about 2 hours and the ticket was 6 cuc.
To go back to Havana from Trinidad we had the bad idea of taking a viazul minibus which is much faster because it stops just once but also extremely small, the trip was really a hell.
Ok, to Trinidad 300Km, it's not so far but in Cuba that's too much. You can use Via Azul, 25 bucks to get to trinidad in a big bus with air conditiong, bar, bath and TV. There is also another bus company, Astro that will take U for about $17. The buses aren't as conmfortable as Via Azul but they're fine. all this buses take around 6 hours to get to trinidad. You can take also the train but it will take you just to Cienfuegos, 80Km from Trinidad and there U must take something else to get to trinidad, Via Azul $6, Astro $5 and a taxi, around $25. Also the train takes almos 12 hours to get there so if u're short in time that's not a good option. Last but not least, if U have plenty of time, U're looking for some adventure and U're not afraid of maybe sleeping one night in the highway you can go hitch hiking. That's my usual men transportation, it cost me to go till Trinidad usually no more than 20-30 cuban pesos and that's the same as only one dollar... ;)
Once you're in Trinidad everything is different. Trinidad is small so in one day you can walk around without problems. So be sure to take one pair of sandals or conmfortable snickers to walk. There are always all around trinidad bicicles ready to take you everywhere. They are cheap and you also have the option of just discuss the price with owner.