Day 3 : Kirkwall to Tongue : 75 miles, strong north-westerly gale

That wind was still going strong when I got up at 05.30, saddled my bags and put on the lights.
Whilst I received benefit during my 15 mile 'sprint' to catch the Pentland Ferries's 08.00 crossing (need to be there by 07.30) from St Margaret's Hope to Gill's Bay (5 miles west of John O'Groats), it really made the rest of the 60 miles extremely difficult and cold. In fact the joy of getting to the top of many arduous summits battling against the wind was eliminated by the fact that I needed to cycle hard down hill to get anywhere.
Selected engineering highlights of the day for me were:
1. Churchill Barriers

Churchill barriers 1942-45; the roads were diverted to link to the barriers, which were located at the shortest distance between the islands. Presumably these were built to secure Scapa Flow following the early loss of 833 lives on HMS Royal Oak - poignantly commemorated in Kirkwall's Magnus Cathedral I noticed the day before.

Castlehill Harbour - a home of export of sandstone flagstone

2.       Castlehill harbour adjacent to Castletown

The 19th century saw boom years for Caithness as a source of flagstone. Much of the stone was processed in the harbour area of the village of Castletown, and many of the streets of London, Sydney, Edinburgh & the financial district of New York City are paved with it. The harbour was built by James Bremner.

3. Dounreay

Home to the UK's research and development into fast breeder reactor technology, materials etc.
Not a lot to see here except the scale of the place is significantly greater than I had expected. 
I hadn't recognised before there is also a MoD Royal Navy Vulcan Naval Reactor Test Establishment (NRTE) - it looks like is still very much operational.