Caerhays Castle, is located in a sheltered valley overlooking Porthluney Cove on the South Cornish Coast  You park on the edge of the cove which looks over the Atlantic Ocean.
Quote from Head Gardener
The 100 acre garden at Caerhays contains a combination of both spectacular spring displays of enormous tree magnolias, rhododendrons and camellias as well as a huge range of rare woodland trees and shrubs originating primarily from China. It therefore has plenty to offer the more enthusiastic gardeners as well as those who simply want to admire and appreciate the unique spectacle.
A must for lovers of magnolias and rhododendrons.

2009 - Gardens Open.
16th February to 31st May seven days a week 10.00 to 5.00 (last admission 4.00). 
House Open. 16th March to 29th May weekdays only (including Bank Holidays). tours 12.00, 1.30, 3.00 (reservations advised). 
Tearoom, dogs on leads, limited disabled access.

Gardens in Cornwall map