READ MORE Bonnaroo 2009 photo by Katie Stratton/Getty ImagesI'll be honest with you. I have an ulterior motive for publishing my annual guide to outdoor music festivals with a classic rock influence. Oh, sure, I want you to have the information about who's playing where. You might even be lucky enough to be planning a trip to one or more festivals. But as I look outside my office window and see no leaves on the trees, no sunshine, and nothing to compel a person to go outside when the high for the day is going to be in the 30s, I need an escape -- something to remind me that it won't always be gloomy and cold outside. Music festivals have come a long way since the days of Woodstock, Monterey, Altamont, and the original Isle of Wight festival. Imagine if there had been live streams, dedicated YouTube channels, and real-time social media coverage back then. Today, we can come pretty close to the actual experience, even if we aren't able to be there in the flesh. The 2013 guide to classic rock fans' favorite festivals offers 21 good reasons to go outside and play.