Kerrera (accent on the first syllable) is an island just off the coast of Oban. I took a water taxi (12 person capacity, though there were just two of us in the morning) from Oban to the Kerrera Marina, at the north end of the island, a ten-minute ride. Then I walked to Gylen Castle, at the south end of the island, and back to the Marina for the ride back to Oban. Total walking time was 4 1/2 hours.