Cost per tile:30
 Room Health: 100
 Monsters it can attract: None

 The bridge seems like it is just that: - a bridge. While it does function as a means of getting your troops over lava and water, it also has some strategic value.
You should always try to capture any enemy bridge you come across (especially if it's connected to your dungeon), then immediately sell it if you have no use for it. If enemy troops are coming across one of your bridges over lava, start selling  it, causing the oncoming foes to tumble in.