Property in Australia is sold on a "block", which is one unit of land. Blocks vary in size, but as a rule, the closer you are to the city centre, the smaller the block will be - unless you can afford really big dollars, in which case you might be lucky enough to find a good sized one. It's quite common these days for property developers to buy a big block, demolish the house on it, then build 2 or maybe 3 smaller houses on the block. These are called duplexes.
When we got to Perth we didn't know this, and when we started looking around for a place to live, we only looked at houses. In fact, we assumed duplexes meant flats or apartments and snubbed them completely. After seeing a few really dire houses (wallpaper falling off, carpets worn down to the floorboards, etc.) we came across a townhouse by the beach. A "townhouse" in Austalia is generally 2 storey (the majority of Australian homes are single storey), and built as a duplex.
It was really nice, and another couple had put a deposit down, so we put our own deposit down immediately. That afternoon we wished we hadn't because we found another townhouse, a bit bigger and much nicer. We withdrew from the first place and put our deposit down on the other one instead. After a brief delay while the owners moved out, we moved in.
This is the view of the duplex from the street. Our house is the middle one of the three on the block
This is a better view of our house. The balcony looks out towards the Indian Ocean and the block like machines on the sides of the house are the air conditioners.
This is taken from our balcony, looking west. We're about a kilometre from the beach, and at the top of a hill, so if the trees weren't there we'd have a sweeping view along the ocean. The port of Fremantle is just down the coast, so we can sit on our balcony with a pair of binoculars and watch the ships go by. It's rather nice...