Apsidal church in Precentorium
Among the ruins of Vindolanda, a mile castle along Hadrian's wall: this curved room in the Headquarters building was used as a church by the Christians among the legionaries stationed here. It is (I think) the oldest church known in Britain.
Crew 119 will tour Vindolanda, as well as the Roman Military Museum nearby, on their high adventure trip to the UK this month. We leave next Friday.