Sajang Island, also spelled Sayang Island or Pulau Sajang, is a small, uninhabited island in Indonesia's West Papua Province. It is located off of the the northwest corner of the island of Papua, about 50 miles northwest of the island of Waigeo. As far as google maps shows, there is no sign of habitation or other features, just green jungle surrounded by a narrow beach. The island is about two miles across, meaning its area is around four square miles, and at no point on the island can you be further than a mile from the ocean.
Sajang Island would be fairly unremarkable, except for one thing: It is located at 0 degrees and 17 minutes north, meaning it is just barely inside the northern hemisphere. And why this is interesting because Sajang Island is separated from the mainland of Papua by only a shallow sea, and Papua itself is connected to the mainland of Australia by the same shallow sea. Sajang Island then, is the northernmost point of the Australian continent, and the four square miles there (as well as some even smaller islands to the south) are the only part of Australia that peeks into the northern hemisphere. Because of these four square miles of uninhabited jungle, we can say that Australia, like every other continent besides Antarctica, exists at least partially in the Northern Hemisphere.
This might seem like a trick: after all, aren't the various islands of the South Pacific sometimes included with Australia and New Zealand in a "continent" called "Oceania"? Couldn't we claim Hawaii as part of this continent and say that it is the furthest north point? The difference is that the island of Papua, and its own islands, is part of the same continental plate. And indeed, during the last ice age, someone could have walked from the southern tip of Tasmania to Sajang Island without too much trouble. By a reasonable geographic definition, this island lies on the Australian continent.
One of the things that fascinates me about geography is its fractal nature, how a standard definition of a geographical area has smaller and smaller fragments trailing out from it. Outside of the "Australia" that most people think of lies the island of Papua, a part of the same continent that has been flooded by the shallow Arafura Sea. And on the northwest part of that island lies the peninsula of West Papua, and off of that lies the large island of Waigeo, and then off of that lies the small island of Sajang. And for those who wish to go further, a mile off the north coast of Sajang lies an unnamed island, a tenth its size. Although it might seem like a small manner, the existence of this unremarkable island off the northern shore of a rustic province of Indonesia is a sign that in geography, the classifications and borders we put on things often have exceptions that don't occur to us.
(And after researching and writing this, I must admit that there is a possibility that the North Maluku islands, to the northwest, which are much larger and populated might also be considered part of the Australian continent: but please allow me the poetic fancy that the small island of Sajang is the extreme point of Australia.)
(Although its status as a geographical extreme point is not attested here, here is the coordinates of the island)