Castle Farm entrance is down a private drive directly off the A225, halfway between the villages of Shoreham and Eynsford, or via Redmans Lane, near Lullingstone Visitor Centre.
The postcode of TN14 7UB can be inaccurate, and take you to the wrong entrance - so follow local signage, or use this link via Google Maps.
On the what3words app, the A225 entrance is: dusty.tigers.event.