Where to stay
The 3 parts of Havana we got to know are (from West to East) Vedado, Centro Habana and Habana Vieja.
Vedado is a residential area and, away from the main thoroughfares, very quiet. It is an excellent neighbourhood if you appreciate a good night’s rest and are not dying for fiestas and other entertainment (we weren’t). There is a decent amount of restaurants nearby if you want to go out dining.
To get to the tourist places (mainly in Havana Vieja) you can take a taxi or -as we did- make the long trek (about 5 km) along the Malecon. It sounds interesting, but the first part (until you reach Centro Habana) is not that exciting except that it is along the shore. The Malecon is a four-lane road of fast moving traffic which is hell to cross. The footpath on the sea side is in a sorry state with the concrete largely eaten away by the sea water. There is no architecture worth seeing along the road, except if you consider the US embassy as worth seeing. Yet the walk is not really unpleasant.
Centro Habana is, well, central Havana. The houses are a bit like in the old town, but they did not benefit of the restoration effort. You’ll see collapsed houses, ruins where people are still living. There are almost no tourists and after dark it gets a bit dreary. It is probably not dangerous, but you do not feel at ease (we stayed here on our last night before leaving Cuba). Also there are precious few restaurants in this area. It is not too bad if you are close to the Malecon, where there is a festive atmosphere in the evening. We were here on a saturday evening and there were a lot of food stalls on the Malecon, catering essentially for Cubans, at Cuban prices, a world away from the old town that caters mostly for tourists, at tourist prices.
Habana Vieja (old Havana) is where the action is (or supposed to be). As we are not of the action type, we did not venture here after nightfall. Lots of casas all over the place, tons of restaurants and bars, but not much Cuba left.
What to see
Old Havana, obviously, it’s where everybody goes. It is pretty in places, downtrodden in other. I personally did not like the Disneyland atmosphere, with a lot of nicely repainted and reconstructed houses, loads of tourists (not helped by the fact that they are now also being dumped by the boatload as cruise ships are once again mooring at the port next door), bars, restaurants, fancy shops where you would not see a Cuban in a hundred years, but it is nice. Mercaderes is the worst in this respect, with -among other things- fashion shops that are way beyond my budget, leave alone that of the average Cuban.
People come here to recognize the places from the guidebooks, so there is a hell of a queue outside the Floridita where the daiquiri is supposed to have been invented (so what? does it mean it is any better than elsewhere?) while the restaurant next door offers excellent food for half the price and is almost empty.
The Paseo de Marti (or Prado) sits between old town and Centro Habana and is a bit like the local version of the Ramblas in Barcelona.
Unfortunately we did not have time to venture to the fortress on the other side of bay.
How to leave
The Viazul terminal is way out of the centre. You lose a lot of time (and money: you almost certainly need a cab) if you want to take the bus out of town: you’ll need to go here and back to buy your ticket, and back again when you are actually leaving.
We did not figure out where to take the Conectando bus and where it can take you.
However we spoke to the people running our casa and they arranged us a shared taxi, or colectivo to get to Viñales. It picks you up where you live, saves you 2 hours on the bus ride (and that’s without considering the time lost to get the tickets) and is just a bit more expensive (20€ per person instead of 12€, but you do not need an extra taxi to get to the bus station).