Getting there & away
It's easy to reach Sankhu by bicycle from Kathmandu (20km). The road is sealed and flat (with a few minor exceptions), and it's an attractive and interesting ride, once you get past Jorpati. Figure on a 1½-hour ride (11.5km) from Bodhnath.
For a loop trip it's possible (in the dry season at least) to cross the Manohara River near Bramhakhel and climb to the fascinating Changu Narayan Temple. For a longer loop you could cycle or bus to Nagarkot and then cycle or walk down from there.