Although it's a huge city, Havana feels like a collection of neighborhoods -- each with its own small-town character and vibrant market. And a delightful experience is to simply wander through a neighborhood farmers market. Taxis are so inexpensive, we'd just hire one and hand the driver a list of places we wanted to visit (gleaned from our guidebook and advice from our B&B hosts), then enjoy a stop-and-go morning.
(By the way, I'm just starting a two-week series of posts from Cuba. This promises to be a great adventure through a mysterious-to-most-Americans island that's just now opening up to regular tourism. I hope to post twice a day for the next two weeks here on my blog and on Facebook. Please share this with any traveling friends interested in venturing to Cuba.)