Often referred to as "The Dena", Altadena is has been known to attract teenage partying and fun, not to mention quite a bit of marijuana use. Altadena also attracts teenagers from 'boring' areas or suburbs around Los Angeles (such as La Canada, etc.). Altadena is host to a few girls and boys foster homes and half-way houses, and is quite even in population between young people and elderly.
Gravity Hill is located in a "secret" location in Altadena, and Farnsworth Park is a notable landmark for partying, making out, pick-up baseball/basketball/football/soccer games, little league, picnics, and concerts.
Although Altadena has been host to a few gangs, violence is minimal, if there is violence at all. In fact, most violence goes down in Pasadena.
All in all, Altadena is the place to be for a naturally good time. No raves or anything, just good people and cool places to be.