BAINBRIDGE ISLAND — For four hours next Monday, the grounds of Bloedel Reserve will be open, free to the public.

It’s a special and unusual event for the award-winning 150-acre preserve on Bainbridge Island, which typically requires reservations, a $12 general admission and sometimes limited hourly attendance to ensure that every visitor enjoys a tranquil and uncrowded experience with nature.

But this is a special occasion — the reserve is celebrating its 20th anniversary as a public garden.

So from 12-4 p.m. Oct. 13 the public is invited to tour the Reserve’s tranquil trails and marvelous gardens which were created and are maintained under the Bloedels’ converging influence of the conservationist movement and oriental philosophy.

Prentice and Virginia Bloedel established the garden hoping to capture a Western expression of the essence of a Japanese garden.

Today, the reserve includes a traditional Japanese garden and a rock and sand zen garden, in addition to many other natural amenities including a moss garden, a rhododendron glade, sweeping lawns and woods, numerous lakes and a French chateau-style mansion of a visitor’s center.

On the day before the garden is open free to the public, Bloedel Reserve’s executive director Richard Brown will present a free lecture and slide show titled “From Agate Point Farm to Bloedel Reserve: The Evolution of a Public Garden” at 2 p.m. Oct. 12 at Island Center Hall, 8395 Fletcher Bay Road on Bainbridge.

Also check out historical photographs of the reserve hanging throughout the month at the Bainbridge Island Historical Museum in Winslow.

Info: www.bloedelreserve.org.