You can drive all the way to the top of the drive, just ask the lady on the gate, who will open the gate for you...the bottom part of the garden is flat (with grass and gravel) and you can see most of the garden from the bottom. and the garden cafe is at the bottom..
There are pictures on my website thegiantshouse
Hope that helps, and hope to see you here..
Ah, I see others have answered this question. I spent two months in NZ without driving, there are good bus services, and as mentioned, Akaroa shuttle and French Connection from Christchurch to Akaroa. Akaroa itself is a great walking town, no need for a car.
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