There are three half day and full day tours in Darwin, the first is the Darwin City Sites tour with AAT Kings is a small group tour that will let you see the Aviation Museum, a B-52 Bomber, footage from the WW2 Japanese air raids, the Museum and Art Gallery, Aboriginal art, and the Botanic Gardens, all in a half day. There’s also the half day Jumping Crocs & Nature Adventure, which is a spectacular crocodile viewing cruise down the Adelaide River, and finally the Katherine Gorge Cruise & Edith Falls guided tour, which is a 1 day return trip from Darwin to Katherine Gorge. If you have more than 1 day, there are plenty more Northern Territory tours that leave out of Darwin to explore best the Red Centre has to offer.