Riders travel slowly on themed boats along an artificial river that meanders through decorated caves and tunnels featuring different themed scenes of lighting, sounds, props, animatronics, or other visual effects. The boats drift along on a gentle current, typically generated by a paddle wheel. This type of amusement ride became relatively common at amusement parks across the UK and the USA in the mid-20th century. The concept of the river cave is also very similar to those of the early scenic railways in that they attempt to be both educational and entertaining.