Cornwall’s magic is in its coastline. Dramatic cliffs combine with sandy beaches and the occasional ruin for some monumental views that are fairly unique in Britain. You also stand a better chance of getting sun here!
Most of the best things to see are related to the sea. Two of the country’s most dramatic seaside castles are here: the romantic ruin of Tintagel (complete with King Arthur myth) and the noble St. Michael’s Mount (once monastery, now aristocratic home). Charming villages like Fowey, Polperro and Mousehole demand to be lingered within. There’s a real "beach bum" feeling here, with lots of nautically-themed pubs, fishermen selling their wares from the quayside and kids pottering in the in-harbour beaches revealed at low tide.
For more sophisticated beach towns, check out St. Ives. This has been a mecca for artists for more than a century; obvious in its galleries and the slightly more fashionable feel about town. You’ll also find the southern extentsion of the Tate Gallery here, in a dramatic modern building overlooking the sea.
Though they’re inland (seaside living is a fairly modern trend), two major historic houses are worth a detour: Lanhydrock and Cotehele.
Quick Tips:
Read Daphne Du Maurier before you go. She is THE author of Cornwall, and reading her atmospheric accounts of the county will enhance your visit. Everyone knows "Rebecca" and "Jamaica Inn" … you can even visit the latter. I’d also recommend "The King’s General", which does a great job of telling the story of Cornwall’s unique role in the English Civil War.
Avoid Land’s End. It’s a tacky amusement park and tourist attraction. Unless you have a burning need to stand precisely on Britain’s most southwesterly point, you’ll find more interesting and pristine coastline elsewhere.
A couple of the things I plan to do next trip:
1) Go to Rick Stein’s restaurant in Padstow. Stein is one of the UK’s biggest TV chefs and his restaurant is supposed to be great. I haven’t made it there yet so can’t give a personal recommendation. Obviously, book way in advance.
2) The Eden Project (tropical gardens beneath domes in a re-claimed clay pit) has become one of Britain’s most famous attractions since it opened two years ago. I’ve heard that you should also book in advance, avoid heavy tourist seasons and go early in the morning.
Best Way To Get Around:
I’ve always had a car. While it takes a long time to get down there from London, once you’re over the Cornish border the county seems quite manageable. The major highways are good but be aware that many of the tourist attractions are down single-track country lanes. If you’re an American driver you’re going to have to get used to the drill of noting where the "pull over" spots are, then figuring out who’s going to move into one to let the other driver by.
This sounds frightening, but there is a payoff. These little lanes are beautiful, especially early in the season when the stone walls, covered with turf, explode with little spring flowers.
It is possible to get to the major sights by public transportation, though it may take longer. There’s a train from London to Penzance. A lot of people come down just to hike the South West Coast Path, which allows you to ring the entire peninsula on foot.