Great outdoor spots to exercise in DC

Due to the cakes, cookies, pies, sour gummy worms, Yo Crunches, Garrett's popcorn, sour peach rings and multiple cups of Tangy Sweet yogurt my waistline is beginning to suffer, so I need to start some type of exercise regimen pronto. I also think that my youth is wasting away before my eyes and I would like to start some type of exercise routine before my metabolism begins to slow down. You're probably wondering, "Ashley, why don't you take your behind to the gym?" And I would reply to you: "One, because I don't want to and two, because I'm allergic to the gym". Okay, so I'm not really allergic, but I absolutely despise it. It's the most boring thing I have ever experienced in my life. Unless I could watch Justin Timberlake, David Beckham and TJ Holmes simultaneously work out shirtless in front of me then I really don't find it interesting. I like doing activities, such as tennis and....uh....I bought a yoga mat a few weeks...well...two months ago. The bottom line is I need to stop being lazy and just get up and do something. I know I won't be a hardcore exerciser, but I would like to walk/jog and take a yoga class four times a week. My roomy, the yogi-in-training has the scoop on the yoga studios (check out her blog), but where are some good spots to do an outdoor walking session? PLEASE don't tell me Rock Creek Park, I like my life and plan on keeping it for awhile so I don't want to take any chances by going into that urban forest alone where I don't get cell phone reception in some places...NOT cute. So please give me any suggestions you may have, gracias.