There are several museums and galleries in central Havana - all walking distance from the Capitolio building. The cigar factory and museum is just behind the Capitolio, there is a great museum in the old presidential palace that has, amongst other things, the original Granma yacht that the revolutionaries arrived in Cuba on. And across the road is a very good modern art gallery.
Across the harbour is the fortress. This is definately worth visiting as it has a lot of history if that's your thing. It's easily accessible by getting a ferry from the ferry terminals in the old town. Once on the other side of the harbour you can walk to the fortress (20-30 mins) or you can take a taxi.
Hope this helps about 7 years ago
Look for Jose Grillo, he is an amazing Cuban artist in Havana, although I think he might have left for the US. He may still have some of his work at his home/gallery which is near the tourist market in Old Havana. Sorry, can't remember exactly where it is but we found him by asking other artist in the market. about 7 years ago