On the south western side of Loch Caolisport, there is a ruined Chapel and behind that, a cave. This is known as "St Columba's Cave"
St Columba (c520 to c600) was an aristocrat who founded Celtic Christianity in, among other places on the Irish Sea, Iona. This particular Cave is on the shore of that sea, and it is not ridiculous to think that, indeed, it was first used by that Saint.
Inside the cave there is still the remains of an altar. The cross scratched onto the wall a very long time ago has been emphasized with white colour in modern times.
Marion Campbell of Kilberry produced a lovely booklet in which (on page 13) there is a description of this site. I have reproduced her "Mid Argyll Archaeological Guide" in pdf form in Knapdale People. Before the Reformation, this Cave and its Chapel would have been a major pilgrims' destination.