The most common form of Augmented Reality is that of sound or audio. This is where a sound is played, or augmented, over the sound you are hearing naturally. Normally this is achieved by having a handheld audio device where you key in numbers that correspond with numbers on presentation boards around the site. Otherwise, this can be achieved by having an audio track that is downloadable to an ipod/MP3, or on a mobile device.
An example of Augmented Reality mobile applications in York is the audio tours by the Institute for the Public Understanding of the Past (IPUP). Part of the University of York, IPUP has produced three audio tours for York.