The following are instructions left by my Airbnb host:
"The map below shows the quickest route to the beach (via the cow field). This walk takes approx. 3 minutes. The resident cow living in the field is not a problem to walk past (if he is not hassled). Gates open to a dirt field with a dirt track off Jalan Danau Tamblingan. Follow the track to the beach. Do not hassle the cow."