Coll covers about 29 square miles, being some twelve miles long and between one and 3.5 miles wide. Coll is fairly flat and the interior is rocky, particularly to the north of the island. On the summit of Ben Hogh, the highest hill on Coll, is a natural formation of stones, with a boulder set upon three smaller stones - so that it can he rocked.

There are many prehistoric sites on the island, including the cairn at Druin an Airidh Fhada and another north of Arinagour, the standing stones at Totronald, and several iron Age forts and duns, including Dun an Achaidh, which although very ruinous is the best preserved.

The island was held by the MacDonald Lords of the isles, but on their forfeiture passed to the MacLeans of Coll, who held the property until 1865, although only after battles between the MacLeans, MacNeils and MacDonalds. There is a medieval castle at Breachacha, possibly built by the Lords of the Isles, with an 18th-century mansion close by. The island supported a population of 1162 in 1801, but by 1891 this had dropped to 522-while there were between 6000-7000 sheep on the island and 1000 cattle-and now only about 150 people live on Coll, One of the abandoned townships is at Sorisdale.

Breachacha Castle: On the edge of the bay, Breachacha Castle, built in the 14th century. The island was given by Robert the Bruce to Angus Og MacDonald of the Isles, but changed hands between the MacDonalds, MacNeils and MacLeans. A new mansion was built nearby in 1750 for the MacLeans, and the castle became ruinous. Dr Johnston and Boswell visited in 1773. The property passed to the Stewarts of Glenbuchie in 1856, but the castle was bought and restored by a descendant of the MacLeans in 1965.