Not exactly what i will call interesting but i think its the
only "legal" route to get to Sengkang from Pasir Ris by cycling.
Illegal meaning cycling on TPE. Its illegal right? 
From Pasir Ris Park, Downtown East area:
Pasir Ris Dr 3, Pasir Ris Dr 12, Tampines Ave 10, Old Tampines Rd,
Tampines Rd, Hougang Ave 1, Hougang Ave 8 (Punggol Park), Hougang
Ave 10, Punggol Road.
Enjoy