1. Bukit Timah Nature Reserve — Bukit Timah
Singapore's highest natural hill, in a 163-hectare patch of primary rainforest.
NParks lists Bukit Timah Nature Reserve as 163 hectares and open from 7am to 7pm. Bukit Timah Hill, at 163 metres, is Singapore's highest natural peak, and hiking trails lead to the summit. The visitor centre is at the end of Hindhede Drive, where guided tours and workshops are held.
NParks's page notes demolition works at the summit scheduled from July to March, so check the linked notice before you go. Hindhede Nature Park is next door if you want a shorter, gentler walk.
Good to know: Start at 7am to beat the heat and the crowds, and keep food out of sight because of the macaques.
NParks Visitor Centre, 177 Hindhede Drive, Singapore 589333