On one of the episodes they got on a small boat and headed out to an island just off the mainland - there are probably a few to be fair.

The last one ferry I got on was a Western Ferries across the Firth of Clyde to Argyle - luckily we got our tickets in advance, but it can be pricey for a half hour journey if making a return trip with a family (www.western-ferries.co.uk/mob/fares.shtml).
There are some great views and we saw a small pod of porpoises at one point on one of our journies.