"The whole of Cantyre, indeed the whole of Argyllshire, and all of the Western Isles are monuments of early Christianity. The very names tell you that. You can count the names which begin with 'Kil' by the score, and 'Kil' means 'cell', a place where early missionary priests established themselves...." Isle, Ben and Loch, from the Clyde to Skye. S Heckstall Smith, Edward Arnold, London, 1932.
Spoiled for choice I would say — from a famous abbey to a pile of medieval stones via classic 19th Century Church of Scotland small churches and a couple of Roman Catholic chapels (Drimnin, and on Canna). So where to begin? I guess with the medieval chapels, some with graveyards, separate burial grounds (or cemeteries), and ancient crosses — there are loads in various states of ruination at the following anchorages:
Ardminish Bay, Gigha: St Cathan's chapel and graveyard
Bàgh Dun Mhuilig, Loch Craignish: ruined chapel and graveyard
Balnahard Bay, Colonsay: a very ruined chapel and eroded cross
Balvicar, Loch Shuna: Kilbrandon Old Parish Church and graveyard
Calgary Bay, West Mull: Cladh Mhuire, burial ground
Canna, North of Ardnamurchan: graveyard and cross, Lorne Campbell gravestone
Carsaig Bay, Kintyre: burial ground
Chapel Bay, Loch Caolisport: very overgrown St Columba's chapel and burial ground
Craighouse, Jura: Cill Earnadil graveyard
Dunstaffnage: Lower Loch Linnhe: rather grand ruined chapel, more of a small church really
Eilean Mòr, Kintyre: monkish cave and St Cormac's chapel
Eilean Munde, Loch Leven: the very best of burial grounds, and a chapel
Ellary, Loch Caolisport: burial ground
Inch Kenneth, West Mull: chapel and burial ground
Kilchoan, Loch Sunart: chapel and graveyard
Kilnaughton Bay, Islay: chapel and rather interesting graveyards
Loch a'Choire, Lower Loch Linnhe: graveyard
Loch Aline, Sound of Mull: graveyard, grave slabs in the church
Loch Beag, Firth of Lorne: old parish church of Kilmarie and graveyard
Loch Buie, South Mull: St Kenneth’s Chapel and graveyard
Loch na Cille, Kintyre: graveslabs, chapel
Loch Spelve, South and East Mull: parish church of Killean
Loch Stornoway, Kintyre: burial ground
Nave Island, Islay: chapel
Port Mòr, Aros Bay, Islay: Kildalton old parish church, and cross
Toberonochy, Loch Shuna: chapel with graffiti, and graveyard
There is then a gap of several centuries, spanning the destruction during the Reformation, before the sort of churches we are familiar with started to be built in the late 18th/19th century. Many are very serene and rather nice to visit even if you are of no particular religious persuasion, but need a bit of a sit down and a think. Sadly many are now closed or for sale.
Ardchattan Church, Loch Etive: now closed
Ardfern, Loch Craignish: Craignish Parish Church, now closed
Camus Aiseig, Upper Loch Linnhe: Ardgour Parish Church
Arinagour, Coll: Parish Church
Bowmore, Islay: Kilarrow Parish Church, the round one, for sale
Canna: North of Ardnamurchan: round tower church and the Roman Catholic Chapel
Craignure, Sound of Mull: Parish Church
Drimnin, Sound of Mull: St Columba's chapel
Kilchoan, Loch Sunart: old and new Parish Churches, graveyard
Loch a'Choire, Lower loch Linnhe: Kingairloch Church
Loch Cuan, West Mull: Kilmore (Dervaig) Parish Church, another round tower
Portnahaven, Islay: Parish Church, for sale
Ulva Ferry, West Mull: Telford church
And some grander stuff:
Ardchattan, Loch Etive: ruined Priory
Iona, West Mull: Abbey and Nunnery — a magnet for tourists, but remarkable
Oban, Firth of Lorne: St Columba's Cathedral (20th century)
Port na Moralachd or Achnacroish, Lismore: Clachan Kirk, surprisingly a previous cathedral
Oronsay, Colonsay: extensive and well preserved ruin of a priory
And finally, there is a great monastic site with monkish beehives, more or less unique to the area, on the Garvellach Islands, Firth of Lorne.
