An invisible notice board
The Ship-of-Fools internet website famously lists reports on church services by 'mystery worshippers'. This provides a bit of fun for us all, but can at the same time be quite thought-provoking. The 'mystery worshipper' kind of activity can also be carried out more academically with serious theological studies in mind.
Noel Heather is an academic in the University of London who researches Christian poetry of the Reformation era and Christian language of today.