Cornwall can be very wet. One year it seemed to rain non-stop for two years! What's been said above- all true- depends where you are based. Don'
t rule out Kingsand/Cawsand, and Fowey is lovely too. St Mawes/St Just-in -Roseland- these are all on the quieter, greener south coast and well worth a visit. Plenty of places to eat, depends what you want to pay, how far you want to drive.
If you're interested in plants the Eden is a given, but you might find the Lost Gardens of Heligan a much better, less-touristy experience. Get down a tin mine at Geevor, fascinating tours conducted by former miners. Walking boots on and walk from Sennen Cove- round Lands End (avoiding the cack) and up to Porthcurno- magic. Coffee in the MInack Theatre cafe/museum then catch the open-topped double decker bus back to Sennen Cove.