Cross the Coronation Bridge at golden hour

The bridge is remarkable at any time of day, but late afternoon is the pay-off. From roughly 4pm in winter (5.30pm in summer), the light turns the red girders rust-orange and picks out every ridge of the Teesta gorge. The best viewing angle is not actually from the bridge itself but from the laybys on the Mongpong side, where you can frame the full arch against the river and, if the haze lifts, the outline of Kanchenjunga behind. Bring a polarising filter if you own one; the glare off the river is vicious.
A second, less-visited vantage is the Sevoke Railway Bridge (a separate, older iron structure about 2km downstream) which you'll glimpse through the trees from NH 17.