Population: ~ 10 million
Telephone dial code: 021
Airports: Galieão (International) and Santos Dumont (Domestic)
Rio is a casual and relaxed city where less really is more. Lots of people try and reduce Rio to a catch all sound-bite, but we aren't going to join the list of failed efforts here. Rio has to be experienced to be believed. What ever you think you know or perceive about this city will be quickly turned on its head once you arrive.
Blend in easier by wearing beach clothing and flip flops (havaianas) and choose the ones without the heel strap. If you do feel intimidated by people looking at you put your camera in a plastic super market bag - which will also handily keep it dry in a rain shower. If you would like to visit a Favela Community (and there's no real reason why shouldn't - tourist dollars are always welcome.) make sure to get a local to show you around or take an organised tour. There is a chance of negative experiences should you walk in by yourself and start taking photos.
Prices for hotels and apartments increase dramatically during the carnaval fortnight and approach advanced economy prices. The Rio experience is much more than the carnaval so unless you specifically want to see the main parade in the Sambôdromo we would recommend visiting outside of the carnaval period.
Copacabana district has the most foreign tourists and some people will find it seedy, especially at night. If you get there and find it's not to your taste, take a taxi to Ipanema, Leblon or Barra which are more up market and the later has 15km of beach and very few foreigners.
The Cariocas (natives of Rio) are charming people who are fun to hang out with. The middle / upper class of Zona Sul (where you will be) can be insular and you may find it more difficult to tap into the social pipeline here than in other Brazilian cities.
The must see sights and activities include: Sugar Loaf Mountain (Pão de Açucar); The Statue of Christ (Christo Redentor); Republic Museum; Hang gliding; Rocinha tour; any Samba School; a Flamengo / Vasco home match at the Maracanã; a night out in Lapa; the New Year festival and don't forget the beaches !