Anything less than three days in Rio  is sheer absurdity. A week will give you time to explore museums and historic sights, shop, and lounge on the city’s famous beaches as well as take a day trip or two to the surrounding beaches or mountains of Rio de Janeiro state .
Despite the great variety of its attractions, Rio de Janeiro state is extremely compact in size. Whether you’re headed to the mountains or the sea, most sights are usually only two or three hours away. While some of these destinations (such as Petrópolis  and Teresópolis ) can be visited as day trips from Rio, it would be a crime to rush when faced with such intense natural beauty and such utterly relaxing environs.
Two or three days reserved for the mountains surrounding Petrópolis and Itatiaia  and another couple (at least) for the beautiful beaches of Búzios and Arraial do Cabo  (north of Rio) or Ilha Grande  and Paraty  (south of Rio) will give you adequate time to unwind and explore.
Tourists visit Rio  all year-long, but there are several factors to consider when planning a trip here. In summer (December to early March) Rio sizzles—both figuratively (festivities and nightlife  are at their zenith) and literally (with temperatures hovering around 40°C/104°F and lots of sticky humidity). If you can’t stand the heat, make sure you have an air-conditioned hotel, or head for the (much cooler) hills. Another option is to visit in the winter (June to September), which is a lovely time. The sun is less intense and the beaches won’t be quite so crowded (at least during the week). Moreover, nights are comfortably cool (around 15–20°C, 60–70°F). The cold fronts that come up from Argentina, bringing cool winds and rain that can last for two or three days, are the only thing to look out for.
Rio enjoys a considerable amount of precipitation (all that lushness wouldn’t exist otherwise) throughout the year. Between March and May, rains are particularly frequent, as well as in December. If you want to take part in either of Rio’s most famous and fabulous festivities—Reveillon  (New Year’s Eve) and Carnaval —be prepared to, first of all, have deep pockets and, secondly, make flight and hotel bookings many months in advance.