If you're also keen on museums, or want to escape the heat, have a look at Museums in Bangkok.
Relax in Lumpini Park | สวนลุมพินี
Big city getting on your nerves? Then go to the park. Even though located in the city, you'll hardly notice anything of the hectic life outside the gates. Green grass (yes, you are allowed to sit on it!!), palm trees, exotic plants, a pond with rowboats for hire… The best place for a break. [Enclosed by Ploenchit, Wittayu (Wireless), Rama 4 and Ratchadamri Road]