Road Trip to Cornwall is a more convenience way to explore Cornwall in my opinion as the attractions are a bit all over the place. Although there are trains and local buses but some places are hard to reach. As my experiences are all by car so I cannot give you an Itinerary with public transports. However, if you gonna drive, here is a 3 days road trip Itinerary for you as a reference!
Day 1 London > Eden Project
Its take around 5 hour drive from London to Eden Project, you should aim for at least half of a day to spend in Eden Project as there are so much to do there. You can add an extra day to it if you have the days off as you are probably tired to walk the whole park and garden after 5 hour drive! St Austell and par have a lot of BnB and nice restaurant, you can stay there for The Lost Garden of Heligan the next day.
Starting your day with the fresh air in The Lost Garden of Heligan, you can enjoy your whole morning in the nature. After that head to St. Michael’s Mount with a stop at Truro to see the amazing Truro Cathedral! Arrives at St. Michael’s Mount in the afternoon by taking a boat to cross the sea. Walk around at St. Michael’s Mount till the tide go away and the CAUSEWAY open! Enjoy your evening with the beautiful sunset in the beach! Stay and dine near Penzance for the night as there are loads of seafood restaurants!
Starting your day by visiting the Minack Theatre, a spectacular theatre carved on a cliff with the sea of the Atlantic Ocean as a backdrop. Then, head to England most western point, the Land’s End with beautiful view of the coastline. After that, you can either enjoy the walk neat the coastline or head to Geevor Tin Mine like me for an excellent experience before going home!