I loved my four-hour private bike tour with David, who was friendly, easy-going, and super-knowledgable about the city's history and politics. We rode to areas I'd never have seen otherwise -- one of the last neighborhoods that hasn't been inundated by tourists, a developing high-rise/high-tech industry area, the beach . . . We were lucky to have perfect weather. In addition to providing some relief from the tourist throngs around the major sites (that of course I thronged to myself), the tour provided a great overview of the city and its culture. The cycling is far from strenuous and there's hardly any riding in car traffic; there's lots of stopping to check places out, hence lots of starting up again. Basic bike-handling skills and comfort on a bike are all that's needed.