It is not a problem to get there unless you are American or live in America. Still there are no impossible things! You have few options:
1) Fly via Mexico, Canada or Bahamas.
I flew via Bahamas (Nassau) and although there is not much to do there you can spend nice day on the beach. From Nassau you can fly to Havana with either Bahamas Airlines or Cubana Air.
Booking the flight to Havana from US is tricky. On the website you can book only about 3 weeks in advance. If you want to book earlier (and you should especially if you going in high season) you nee to write them an email ( comercial@vacacionartravel.com ) and they will make the booking. You credit card will be charged by company in France. You will than be able to get kind of confirmation from their website (not a real ticket though). Price if fixed all year long - its about 280 USD. There is only 1 flight a day 5 times a week (they dont fly on Tue and Sat). ALthough the whole thing seems to be doggy it actually works!
In Cuba you have a great oportunity of staying with Cuban people at their houses. Rooms for rent are called CASA PARTICOLARES and you can find them all over Cuna. Price for the room is from 15 to 25 CUC in Havana. For additional 3-5 CUC you will also get a breakfast. Every room like that must be registered and the owners have to pay to Govermant monthly quite a lot of money regardless if they have clients or not, thats why price is not negotiable. All rooms are doubble and it is not allowed to let 3 people stay in one room. 1 in 100 they will let you do it. There are unexpected controls and if they get cought they can get in troubles. I highly recommend staying in Casa Particolares - they are save, clean and most importantly you have a chance to meet Cubans and see how they really live!
You need to prove on Cuban border that you have accomodation booked for first 3 nights. Confirmation from Casa Particolares is sufficient.
If you don't mind spending lots of money stay in beatiful NACIONAL Hotel.
HOTEL NACIONAL de Cuba
Calle O esquina a 21, Vedado, tel (537) 8363564, reserva@gcnacio.gca.tur.cu
Elegant, beatiful, with great see view, has nice lobby, bar and swimming pool. Sometimes anoying groups of tourists but on the other hand Frank Snatra, Winston Churchil and many more famous people were guests here. Great for a drinkin the evening in outside bar area.
Casa Particolares CONCHITA GARCIA
Calle 21, nr 4, e/N y O, El Vedado, 7th floor, Apt 74, tel (537) 832 6187, mob (05) 291 5729
conchitagarcia21@hotmail.com, conchitagarcia23@yahoo.com.mx
Very clean, big nice roomand good breafast. A bit lazy and spoiled Conchita but if you get to know her better can be funny. The building is beatiful and it is just on the oporite site of the O street, 1 min walk from Hotel Nacional, which makes it perfect location. You not only have all practical things (international phone, exchange, car rental) but also bar and swimming pool. As tourist you can enter anywhere and anytime in the hotel regardless if you a hotel guest. Great to have a swim in the morning and drink in the evening. You kind of live in Nacional for 1/10 of the price.
HAVANA VIEJA -grab lunch at El Patio or Taberna de la Muralla. it is not enough to walk the touristy/renovated part of the streets. You have to get off the "lonely planet" walking tour track and go into small streets where you can see real Havana...be careful though as it is not as safe. Do not have to many things hanging and hold to your camera tight! There are instances of rubbery - we heart about it and we experienced it! After that have a Mojito in La Bodeguita del Medio.
MALECON - walk along to see the sunset
MUSEO DE LA REVOLUCION - if you do not speak Spanish its kind of hard as there are very few descriptions translated to english. Might be useful to take a guide.
CENTRO HAVANA - Capitolio Nacional and around.
VEDADO - swim and drinks in Hotel Nacional, ice cream in famous COPPELIA, American consulat with 148 flags in front covering
PLAZA DE LA REVOLUCION
LUNCH:
EL PATIO
TABERNA DE LA MURALLA
DINNER:
EL ALJIBE - 7ra Avenida, on the corner of Calle 24, Playa. 2041583
A bit chease decor but great for big groups, the house special is unlimited roast chicken with rice, beans and salad. Toby wrote: "its unlikely you will find better chicken anywhere in the world" and I could not agree more. It was the best one I had so far...
LA GUARDIA - Concordia No.418 e/ Gervasio y Escobar, Centro Habana, www.laguardia.com
The Guardian wrote: " the greatest and most magical is La Guardia, so magical that it is temting to protect it by withholding its address...". Known from famous "Strawbery and Chocolate" film, AMAZING interior and atmpsphere, great food. Book in advance.
You will arrive to Trinidad in the evening.
There is also great night life in Trinidad so believe me that eventhough you are there for 3 nights you will not be borred.
EL Mirador bar with great views and good mojitos
It is also worth to drive by Hotel Los Jazmines 4 km away from Vinales. This hotel has one of the best locations in Cuba - you can get postcard perfect view of the Velle de vinales. The minus is that lots of other tourist want to take the same photo so its really crowded thus i dont recommend staying to long.
If you decide to stay overnight you should eat at your Casa Particorales - there is not that many restaurants in Vinales. As in every other city also in Vinales there is Casa de La Musica where you can dance salsa under the stars. In my opinion not as good as in Trinidad.