Quito lies between two mountain ranges and its altitude is 2,800 metres or about 10,000 feet. It may take you a couple of days to get accustomed to the altitude.
Quito is roughly divided into three parts:
the Old City at the centre, with southern and northern districts to either side. The greatest concentration of tourist facilities is in the North, including the airport. Quito's Old City is the largest in the Americas. It has undergone a huge restoration and revitalization program over the last decade, mainly financed by the Inter-American Development Bank. It boasts no less than 40 churches and convents, 17 squares and 16 convents and monasteries. It's been called the 'Relicuary of the Americas' for the richness of its colonial- and independence-era architecture and heritage. It's a great quarter to wander, with several excellent museums and plenty of restaurants and terrace cafes for a rest while sightseeing.
Modern, northern Quito (on a map, up until the southern tip of the airport) is a fun place to explore, with plenty of museums and urban parks as well as restaurants and nightlife. The southern and northern (from the airport up) districts of the city are more working class and seldom visited by tourists.