Perdana Botanical Garden
You could spend hours walking around the Perdana Botanical Garden (depending on how hot it is).
The Bamboo Playhouse is particularly lovely, and while some other areas are a bit run down, it’s definitely worth a visit.
There are shaded areas to help avoid the sun, but I’d still advise not going at midday, and definitely bringing some water (or 100 Plus).
Located near the Masjid Negara and the Islamic Arts Museum Malaysia.
Free entry