Although it can't rival Buenos Aires or Rio de Janeiro, Santiago buzzes with increasingly sophisticated bars and clubs. Santiaguinos often meet for drinks during the week, usually after work when most bars have happy hour. Then they call it a night, as most people don't really cut loose until Friday and Saturday. Weekends commence with dinner beginning at 9 or 10 and then a drink at a pub. (This doesn't refer to an English beer hall; a pub here is a bar with loud music and a lot of seating.) No one thinks of heading to the dance clubs until 1 AM, and they stay until 4 or 5 AM.
Bars and clubs are scattered all over Santiago, but a handful of streets have such a concentration of establishments that they resemble block parties on Friday and Saturday nights. Try pub-crawling along Avenida Pío Nono in Bellavista. The crowd here is young, as the drinking age is 18. To the east in Las Condes, Paseo San Damián is an outdoor complex of bars and clubs. It's a fashionable nighttime destination.
What you should wear depends on your destination. Bellavista has a mix of styles ranging from blue jeans to basic black. Paseo San Damián maintains a stricter dress code.
Note that establishments referred to as "nightclubs" are almost always female strip shows. The cheesy signs in the windows usually make it quite clear what goes on inside.
Once mostly underground, Santiago's gay scene is bursting at the seams. Although some bars are so discreet they don't have a sign, others are known by just about everyone. Clubs like Bunker, for example, are so popular that they attract a fair number of nongays. There's a cluster of gay restaurants and bars on the streets parallel to Avenida Pío Nono in Bellavista. There's not as much for lesbians in Santiago, however, although some women can be found at most establishments catering to men.