Unfortunately Heronswood is no longer open for visits. The property is for sale see: http://pnhc.org/
There are some other great gardens to visit such as the Dunn Garden and the Miller garden. They are close to each other and both require advance appointments to view. There is the Blodel Reserve and Little and Lewis Garden, both on Bainbridge Island. Not sure about the Blodel but you need an appoint. for the Little and Lewis garden. They may be able to give you leads on other gardens on the Island you might be able to see. You might also contact the Northwest Horticultural Society for other options. I have supplied a link below for photos of Heronswood. There are also many other private gardens on my photosharing site. Happy travels!

Here is a link that might be useful: http://public.fotki.com/BambooMary/my_green_house/botanical_gardens/heronswood_visits/

thank you