If you find yourself as far north as this I'd highly recommend the Highlights Tour from John O'Groats Ferries.
The ferry journey itself was lovely with the kids spotting puffins, dolphins and seals. Once on Orkney we quickly found our coach for the tour of the island. No separate tour guide and driver here, the driver does both, speaking through a headset. I was a bit sceptical of that but he was actually excellent and knew the history of the island back to front while still being engaging for young and old.
The tour covers all the major visitors spots on Orkney: Kirkwall, Churchill barriers, Scapa Flow, Skara Bray, Ring of Brodgar etc. At each spot there was adequate time to get out and have a look around.
Bear in mind that Skara Brae entry is not included in the ticket but is cheaper buying from the ferry office than when you get there. You woudn't want to miss it.
Final highlight of the trip was the wonderful Italian Chapel built by WW2 prisoners of war.
I went with my wife, mother in law, and kids aged 12, 9 and 6 so wide tastes to cater for but we all thoroughly enjoyed it.
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