Combining digital reconstruction with mobile technologies has the potential of enriching visitors experience to historic sites. Through designing a mobile App with Google Cardboard it is possible to use technology already in peoples' pockets to provide immersive on-site exploration of historic sites. This paper looks at our experience in developing such a mobile App which acts as a digital guided tour of the remains of St Andrews Cathedral. The App brings together traditional media such as audio, images, panoramas, 3D video and 4π Steradian (or 360°) video with a mobile smartphone and Google Cardboard to provide a tour of one of Scotland's most important historic sites. The mobile App is available from both Google Play and iTunes, providing direct delivery to a potential audience of millions. It complements the location-aware mediaeval St Andrews App, which provides a guided tour to the town of St Andrews as a whole. In the absence of Google Cardboard the App is still useful providing both visual content and audio commentary on this historic monument.