It's really a pretty simple concept; a device that makes it easier (or just possible) to get from Point A to Point B. Why, then, is every bridge different? Sometimes the bridge simply adds to the photograph. Sometimes the bridge makes the photograph.
I'll be pretty liberal here and include anything that keeps your feet dry by passing over rather than through water, mud, or soft ground, such as a fishing pier or boardwalk in a swamp.
Most of these aren't renowned. Each one, however, was certainly worth the few moments required for the photograph.
Yes, I really DROVE across this bridge (September, 1973); didn't scrape anything, either. Dewey Bridge over the Colorado near Moab, Utah. Destroyed by a fire caused by a child playing with matches in April, 2006.