In the heart of this small island nation sits a very good and technical jungle singletrack trail; the Bukit Timah Mountain Bike Trail.
Note that is a single direction trail (clockwise) that offers many points to jump into the trail. It can get very crowded on weekends with a high variability of rider ability, so use caution.
The trail was rebuilt in 2014 to traditional singletrack and has several steep rock drops, rock gardens, roots and tight turns in a lush jungle forest.
This 5-mile loop can only be ridden clockwise, but it offers tons of technical rocks, roots, drops, and switchbacks throughout a jungle environment.
The best way to access trail is from the Bukit Timah Nature Parking Lot off of Hindhede Road. The trail gets crowded on weekends so you may have to park in other areas and link back up to the park. There are maps at parking lots which allow you to get the layout of trail. It's fairly simple if you stay on the well-used trail going clockwise. Additionally, the MTB Project mobile app is useful if you have Singapore downloaded.
Halfway through you'll enter an open meadow that is an old quarry whose rocks built many buildings in downtown at the turn of the century. On Sundays, it's not unusual to see pick up games of cricket and rock climbers working the shear faces leftover from the quarry.