A classic Aussie hike, as Kosciuszko is the highest mountain in Australia and easily accessible. Most people avoid the steep Merritt's Nature Track section that takes you from valley bottom to high plateau - but it is the more interesting and physical section for hikers (i.e. tends to moderate difficulty, whereas the plateau walk is easy). You can catch the chairlift out of the valley to plateau to make it easier. There is a great 360 view of various ranges from the summit. Also consider the track to the summit from Charlotte Pass instead (longer but pretty wildflowers in Spring and far fewer walkers).