PLEASE, for your safety, DO NOT ATTEMPT TO ENTER CAVES. Yanchep's caves are fragile and can easily collapse, injuring you and damaging the caves.

YN-16, better known as Yanchep Cave

Is one of an estimated 540 caves in Yanchep. They were formed over 250,000 years ago by underwater streams from water travelling west from the Gnangara Water Mound to the ocean. The water passed through Tamala Limestone which dissolved and formed caves. Due to safety and conservation reasons, most caves in Yanchep do not have public location information, although with research, some can be found.

Yanchep cave was first discovered in 1903 by Mr J. A. (Jack) Grant. It was further explored in following days by L Ramaciotti, C. P. Conigeave and Harry Kent. In 1937, Yanchep Cave became a tourist attraction but was closed soon after due to safety and environmental concerns. The State Library of Western Austrealia hosts a few images of the cave before it was closed. Take a look at: Yanchep caves - State Library of Western Australia (slwa.wa.gov.au)

You are looking for a small brass plumbing fitting which has been repurposed as a watertight container. You will have to move some small rocks to get to this cache. 

The cache is not inside the cave - it's on the path to the closed off entrance.