Searching the forum will give you plenty of results. It's not that people only now step on the track. And we don't know your preferences either. In terms of nature and serene spots, the area between Bukit Timah station and Buona Vista has something to offer.
All spots that are easily accessible (Bukit Merah station, the bridge near Rail Mall) will be packed on weekend. But just a few hundreds meters further down it's quiet again, though not free of people.