I found this very beautiful park and spent 4 happy hours yesterday. It was too short time so I'll go back one day. It's a huge park and NO Trash! The cleanest place in Bangkok.
Tickets 20 B locals, 50 farang. I don't like double pricing but in this case I don't mind paying 'cause it's so nice place.
"Suan Luang Rama IX (Thai: สวนหลวง ร.9, pronounced [sǔan lǔaŋ rɔ̄ː kâːw], RTGS: Suan Luang Ro Kao), also referred to as (King) Rama IX Park, is a public park in Bangkok's Prawet District. With an area of 500 rai (80 ha; 200 acres), it is the largest park in the city."
https://en.wikipedia.org/wiki/Suan_Luang_Rama_IX
https://www.google.com/search?client=firefox-b-d&q=suan+luang+park+bangkok