Ardnamurchan is one of my favourite parts of Scotland. It's a great full day doing a loop from Fort William and taking the Corran ferry over to the peninsula. Good walking, stunning scenery, trying to spot otters on the beaches, exploring lighthouses and some great cafes en route with lovely, helpful staff. I always drive it clockwise for some reason as for me the most interesting part is the south and southwest.
The islands are also interesting, but the sea maybe choppy in October and they deserve longer than a couple of hours.