Cornwall has an unusually high concentration of National Trust and English Heritage sites (Levant Mine, St Michael's Mount grounds, Tintagel, Pendennis, St Mawes, and more). Annual membership with either organization pays for itself quickly for visitors planning to see 4+ sites, with free parking at many properties an added benefit.
Standard admission to the Eden Project can be upgraded to an annual pass for a modest extra cost, worthwhile for visitors staying in Cornwall long enough to return, or planning a repeat trip within a year.
www.edenproject.comSeveral of Cornwall's celebrated gardens (including Heligan and Trebah) periodically offer joint or discounted multi-garden tickets through local tourism partnerships - check current offers with each garden directly, as availability varies by season.