Lumpini Park (or Lumphini Park) is one of the largest green spaces in central Bangkok. Founded in the 1920s, this inner-city park spans over 500,000 sq m and is home to various flora and fauna. Over the years, it's become a popular gathering spot for Bangkok residents, who would gather for a round of jogging, light workouts, aerobics, and leisure activities throughout the day. Lumpini Park appeals to just about everyone – you'll often find the elderly practising tai chi and couples lounging by the lakeside, as well as 9-to-5 workers relaxing on benches and enjoying exercise in the evenings. On weekends, this green space is often populated by families and the cheery sounds of children.
Lumpini Park's onsite facilities include paddle boats, playgrounds, and an outdoor gym. Before sunset, you can sweat it out at Lumphini Park's free aerobics sessions and high-energy techno tunes. There's also a basketball court if you want to shoot some hoops. Local jazz outfits (sometimes a classical orchestra) often perform during late Sunday afternoons.
http://www.bangkok.com/sport-parks---activities/lumpini-park.htm