Going north there is a serious hill, Lewis has many ancient brochs, stone circles to see.
Harris and Lewis, though named seperately are a single island. Harris is the southern part, Lewis is in the north. Lewis is mostly open moorland, Harris is mountainous but very scenic, the east coast is rocky. The west coast is flatter, with vast sandy beaches. While Harris is hillier than Lewis it is more scenic and you should try to find time to cycle right round South Harris. If however you are going north, and are faced with the choice of cycling up the west coast or the east coast the west is probably the best choice - it's certainly less hilly!
Harris Tweed is cloth that has been handwoven by the islanders of Lewis, Harris, Uist and Barra in their homes, using pure virgin wool that has been dyed and spun in the Outer Hebrides. This is the definition of Harris Tweed contained in the Harris Tweed Act of 1993 and it ensures that all cloth certified with the Harris Tweed Orb symbol complies with this definition and is genuine Harris Tweed, the world's only commercially produced handwoven tweed.
For centuries the islanders of Lewis, Harris, Uist and Barra have woven the cloth: Clo Mhor in the original Gaelic- 'The big cloth'. Nowadays of course it is exported all over the world. More of the cloth is in fact produced in Lewis but you can still see Harris tweed being woven in Harris on the west coast at Luskentyre.
The Outer Hebrides are noteable for numerous lochs. Some of these are brackish and others are dark and acidic, water lillies are quite common and many have populations of trout and charr. Birds include dunlin, redshank, plover, lapwing and the islands are the last stronghold of the corncrake. Nearly every beach seems to have a population of sandpipers. The islands are formed on the oldest exposed rock in the world, Lewisian Gneiss. This is grey coloured with bands of white and dark minerals contorted by the pressure of the earth. These were formed over 3000 million years ago, similar rocks are found today in Canada to which this part of Scotland was once joined.
Going north from Tarbert to Stornoway is a one day ride, passing fiord-like Loch Seaforth. At first it's hilly, with a mountainscape more like Norway than Scotland. Just after you pass West Loch Tarbert there is an long steep climb. The views are splendid when you get to the top, stretching over towards Rhenigidale and Loch Seaforth. Naturally there is a corresponding descent (or climb) on the other side. Once you have passed Loch Seaforth the cycling gets easier. As in the Uists you will find that there are regular bus services with the bus drivers usually being fairly obliging and willing to take bikes.
Generally Lewis is a vast moor covered in lochs and peat. Many loch names end in 'vat' revealing their Norse origin. The west coast is interesting with many things to see, notably the broch at Dun Carloway two miles south of Carloway, and the standing stones at Calanais (Callanish). There is a tea room and shop at Calanais. If you are cycling between Calanais or Carloway and Stornoway you should note that there is a useful back road, still with a good surface, running north of the A858, this is more direct and very quiet.
Try to see the broch at Carloway which is particularly well preserved. Brochs are something unique to Scotland. They are impregnable towers, usually near the sea. There are brochs all over Scotland but none elsewhere. Built from 100BC to AD100, the precise reason for their construction is a mystery. At Arnol is the Black House Museum. This display of how things used to be was lived in up to 1964. North again is Eoropie, the most northerly village in the Hebrides. The 12th century church of St Moluag is here, key in the shop. A mile north again the road ends at the Butt of Lewis lighthouse.
Stornoway, the largest town in the Outer Hebrides, is the centre of Scottish Gaelic culture. Caledonian MacBrayne ferries sail from here to Ullapool (2.6 hours). It has it has hotels, restaurants, B&Bs, hostels and shops.