The handy hop-on/hop-off Habana Bus Tour runs on two routes, T1 and T3 (this being Cuba, there's no T2). The main stop is in Parque Central opposite the Hotel Inglaterra.
This is the pick-up point for bus T1, which runs from Habana Vieja via Centro Habana, the Malecón, Calle 23 and Plaza de la Revolución to La Cecilia at the west end of Playa; and bus T3, which runs from Centro Habana to Playas del Este (via Parque Histórico Militar Morro-Cabaña).
Bus T1 is an open-top double-decker; bus T3 is an enclosed single-decker. All-day tickets for T1/T3 are CUC$10/5. Services run from 9am to 7pm, and routes and stops are clearly marked on all bus stops. Beware; these bus routes and times have been known to change. Check latest route maps at the bus stop in Parque Central.