Cothele House, which is near St. Dominick, if I recall rightly. Cross the Tamar Bridge from England into Cornwall, follow the road through Saltash towards Callington/Launceston ("Lanson" to locals)and turn right and follow the signs off the main road. It is a former stately home and packed full of history and memorabilia, with very polite and knowledgeable staff. The same can be said for Antony House, nearer to Torpoint, which was recently used for the filming of the Tim Burton version of "Alice in Wonderland". If you did not like the film, do not let that put you off. There are many treasures to be seen and a tangible closeness to history.
Take a rainproof jacket and a compass and park your car up on Caradon Hill. You can walk over Bodmin Moor and see the stone circles (The Hurlers) on your way past mining ruins on your walk up to the Cheesewring. From Caradon on a clear day, you can see miles into the distance. Within ten minutes driving distance there is Trethevy Quoit, a neolithic dolman, and King Doniert's Stone. If you drive out to Tintagel, on the North Coast, up close to the English border, you may well pass Slaughter Bridge. There you can see King Athur's Stone, at the place where he supposedly fought his last battle. In some accounts, he struggled from there over Bodmin Moor to return Excalibur to the Lady of the Lake at Dozmary Pool. Unfortunately, the dramatic effect of the moorland lake is now somewhat abated by the fact that it is next to a bloody great reservoir, which effectively dwarfs it! On the main road on the north side, about two or three miles from that, you will find the Jamaica Inn. It is still a lovely building, nicely preserved. Well worth stopping off in for a pub lunch and a pint. If you do go to Tintagel on the North Coast, try to get there when the tide is in. The short drive up to Boscastle is well worth the trouble and this lovely little village, built around a tiny harbour, is so much more impressive when the tide is in. You should also stop at the Witches' House there. It is a wonderful preservation of the original folk beliefs and customs of our island.
Other people, who still live there, can tell you far more. I particularly love the coast road past sandy beaches from Torpoint to Looe, which is still a lovely little fishing village. I am biased, but I reckon that if you can't find something to love in Cornwall, you hardly need to be alive!