Take the BTS (Skytrain) to Phrom Phong station. Walk towards the city along Thanon Sukhumvit for about 50-100 meters. Go into the park and down near the back you'll find this very small free outdoor skatepark. One end has a rolled bank with some ghettoish obstacles, mainly bars and rails, lying around. It's small, hella hot to skate and if you're there at 6 pm you have to stand still whilst the King's song is played for a minute or two, but it's an okay place to kill a couple of hours and meet some of the local skaters.