"Only a Ghost! by Irenæus the Deacon" is a humorous fictional travelogue written by Sabine Baring-Gould. The ghost of Irenæus the Deacon of the church of the 4th century Jerusalem visits London, the "most religious city of the world" in 1870. Baring-Gould described Irenæus’ astonishment on the state of hypocritical, superficial and superstitious "Christianity", and their astonishment in return on the unwarranted thoughts of Irenæus'.