This big park is about 2 miles from the river on Silom Rd. . Go there to relax and get the city out of you. In the morning, folks do Tai-Chi there. Oh baby, step into Oz. Guys with those turned-up toe shoes and funny hats are at the doors.
High tea is also quite the thing to do.
There it will cost you 550 baht though. It is definately worth the 40 baht entrance. I landed up jamming with some kids on classical guitars.