St Martin's Church in Canterbury has been a site of Christian worship almost without interruption since Roman times.
The story goes that when in around 580CE the pagan King ∆thelberht of Kent married Bertha, a Christian princess from Tours in modern France, she insisted that her faith be tolerated, and she worshiped at an existing Romano-British church outside Canterbury.
The Dark Ages aren't called the Dark Ages for nothing, and we have no idea what state the church was in when she arrived. The great Saxon historian, the Venerable Bede, writing in 731CE, states that the church had fallen into disuse, and names it as St Martin's.
Thus St Martin's can claim to be "the oldest church in continuous use in the English speaking world".
There is certainly ample evidence of a Roman building on this site, and there is much Roman brickwork incorporated into the later walls. I like to think that there might have been a small community of Romano-British Christians worshipping occasionally amongst the ruins, during the 170 years between the end of the Roman occupation and the arrival of Bertha.
In 597CE, St Augustine was dispatched to Britain to convert the English. He initially based himself at St Martin's until, having converted ∆thelberht to Christianity, he was able to move down the hill to more substantial accommodation in what became the Cathedral.
Note: To get to St Martin's by car you need to go up Havelock Street and along North Holmes Road. There is no entry into North Holmes Road from the Longport/St Martin's Hill end. There is Pay and Display street parking in the surrounding roads.