Back in the days when I sketched, I'd have a satchel with a camera, paper, pencils, charcoal, conté and ink with me at all times. If I saw something like a drawbridge opening, I'd stop, take a photo, then sketch it as fast as possible, and then take another shot. Later, in the studio, if I liked the results, I'd work it up into a more formal sketch. There was a drawbridge at Seaforth in Sydney - in between where I lived in Glebe and where my mother lived at Whale Beach. It bridged Middle Harbour, a favourite for yachts, sloops and ketches - and it only ever raised when the boats needed to pass under. The drawbridge was set below two rugged sandstone plateaus, much eroded, covered in trees and houses with interesting architecture. The whole setting provided interesting landscapes from many angles.
Unfortunately, I lost most of my works on paper when a storm blew off the roof of my studio.