One of the most adventurous walks on Mull is along the coast west of Carsaig Bay to the natural rock formation of Carsaig Arches at Malcolm's Point. There's a good path below the cliffs most of the way, but near the arches the route climbs and then traverses a steep slope above a vertical drop into the sea (not for the unfit or faint-hearted).
You'll see spectacular rock formations on the way, culminating in the arches themselves: the 'keyhole', a freestanding rock stack, and the 'tunnel', a huge natural arch. The western entrance is hung with curtains of columnar basalt – an impressive place. The return trip is 8 miles – allow three to four hours' walking time plus at least an hour at the arches.