I live in Australia, and I was a cleaner for few years. One of our clients homes was over 100 years old and they had a bunker in their backyard that was accessed by lifting one of the large patio tiles. You then had a three key system to actually enter it. It was tiny, more a bomb shelter if anything, but it was one of the first instances of a bunker that I've ever seen here.

Also, the bunker was mostly flooded, and the owners hadn't decided to clean it out/restore it. It was mostly just a fun conversational point.