I actually am an aficionado of bridges. I've spent countless hours photographing them, often at considerable risk of life and limb. Some of them are such bothers to photograph, what with vehicles and trains interfering with the photographer's concentration.
I even did it for extra money for a while (and still do if you want to count microstock). But mainly I do it for enjoyment. I especially like old, abandoned bridges. There are ghosts there. And sometimes hobos. I learn a great deal from both.
I've also developed a collateral interest in hobo signs and symbols. I plan to document some of those, too, when I have the time.
Rich