A boardwalk (also known as a boardwalk, boarded path, or promenade) is a raised footpath, walkway, or causeway made of wooden planks that allows pedestrians to cross wet, fragile, or marshy soil. They are, in essence, a low-level bridge. Boardwalks can be found throughout the world, especially in tropical climates where they are needed to protect people from getting wet when it rains or floods. Boardwalk bridges are particularly useful where flooding is a problem, such as along the banks of rivers, streams, and oceans. They provide an alternative route to crossing wet ground. A boardwalk also provides a stable surface for walking while allowing water to pass under it. The word "boardwalk" comes from the fact that it was once common practice for builders to use boards for footbridges over ditches and other holes. The boards were attached to the bottom of a vehicle with nails or screws and then covered with gravel or dirt to make a dry pathway for pedestrians or horses. In modern times, plastic mesh is used instead. But the concept is the same: a floating platform for people to stand on while waiting for a ferry or bus. There are three main types of boardwalk structures: tied, chained, and freestanding. Tiered boardwalks are the simplest to build and most affordable.