Canna is the westernmost of the four Small Isles, a long volcanic ridge a few miles north of Rum. The ferry from Mallaig calls on Mondays, Wednesdays, Fridays, Saturdays and Sundays from April to October, sailing across the Sound of Sleat to Eigg, Muck, Rum, and at last Canna. Foot passengers only; no cars. You can take a bike but it isn't worth it, because beyond the single graded lane the island is rough track and sheep trail. From the deck the cliffs of Canna's north shore rise more than a hundred metres straight from the water, the basalt columns stacked like organ pipes. The harbour on the eastern side is sheltered by Sanday, a smaller tidal island joined to Canna by a road bridge that washes out in storms.

The high point at the eastern end is called Compass Hill, and it deserves the name. The basalt that makes the island is rich in iron, magnetised by the long-ago volcanic event that built the Hebrides. Sailing yachts that come too close to the north coast find their compasses swinging crazily; the effect is strong enough that the Admiralty pilot warns navigators away. From the summit, only 456 feet high, the view takes in Rum to the south, Skye to the east, and the Outer Hebrides as a low blue line on the western horizon. On a clear day, which is not most days, you can see thirty miles in every direction.

Campbell bought Canna in 1938, when the island had perhaps two dozen residents and a way of life that was already endangered. With Margaret Fay Shaw, who had spent the 1930s recording songs in South Uist, he began documenting everything: songs in Gaelic, folklore, place names, the names of the small fields, the Latin names of moths he caught in his garden. His scholarship was generous and rigorous. Canna House, where they lived, became a place where visiting scholars and musicians stayed for weeks at a time. In 1981 Campbell handed the whole island to the National Trust for Scotland on the condition that the Gaelic culture be preserved. He died in 1996. Margaret outlived him by eight years and is buried beside him on Canna.

Canna's churches accumulate the layers of Hebridean Christianity. A short walk from the pier stands the Rhu Church, completed in 1914 by the Thom family and known locally as the Rocket Church because its replica Celtic round tower looks like it might launch. It is Presbyterian, but most islanders are Catholic and use St Columba's, which was originally built in the 1770s. Two hundred yards beyond, in a field, a Celtic stone cross from the 7th to 9th century stands missing its arms. The area is called A'Chill, which means "church" in Gaelic; it was probably an early monastery, possibly a daughter house of Iona. Near the cross is a tall dressed stone called the Punishment Stone, with a small notch near the top into which, according to a story for which there is no evidence whatever, offenders had their thumb jammed.

Brown rats, the destructive Norwegian variety, arrived on Canna in the 19th century and by the year 2000 had eaten the eggs and chicks of so many ground-nesting seabirds that the puffin colonies, the Manx shearwaters, and the storm petrels were collapsing. In a methodical and patient effort the NTS eradicated them. The island was declared rat-free in 2008. The shearwaters and puffins are returning. Visitors are still asked to report any rat they think they see, but most reports turn out to be wood mice or shrews. The NTS is now eyeing the rabbits with a similar long-term gaze.