The internet in Cuba is quite rare to find. Most of the apartments do not offer it and only a few hotels or restaurants have it on offer. Basically, the internet in Cuba and Havana works in such a way that you have to buy internet cards for about $2. For a card you will get one hour of internet access. Even then, you usually have to go to big parks to surf the internet. Simply everywhere in the city is not possible.
Basically you should meet the ticket sellers at these parks and be approached by them. But we personally have never seen one of them in Havana. Luckily our hostess bought us some tickets after our arrival.
So it is recommended to buy enough internet tickets as soon as you have the opportunity. And don’t worry that the cards might not work. We never had the problem, or rather it was never due to the cards, but rather to the overloaded internet lines.
The Ambos Mundos Hotel offers all guests the possibility to buy internet cards at the reception, but keep in mind that they only worked in the hotel area – at least in our case. Even if you are not a hotel guest, you can enjoy your drinks on the roof terrace and surf the internet.