Tucked at the bottom of tree-lined slopes along the Kranji Expressway (KJE) is a network of canals that snakes roughly 6.7km from Woodlands Road, through Segar Road, to Bukit Timah Hill. Another network runs 5.8km from Woodlands Road through Bukit Panjang Road to Bukit Timah Hill.

These networks in the northern part of Singapore, and the thick foliage above the 1.7m-deep drains that run next to them, hide a secret - they have been a passage for suspected illegal immigrants who play a game of hide-and-seek with the authorities, and with residents wary of their activities.