There are plenty of outdoor activities in Darwin and the new NT Tourism website has dedicated a huge section to this.
There are detailed overviews on walking (short walks and overnight walks), camping, adventure travel (4WD, crocs and choppers), scenic flights (Darwin, Mary River, Adelaide River, Kakadu & Arnhem Land), rail journeys, river & harbour cruising, fishing, canoeing, kayaking, sailing and even swimming.
There is a myth that you can’t swim in Darwin. There are heaps of swimming options! There are four public swimming pools and four dry-season patrolled beaches. Head to the waterfront where you can grab a boogie board and ride the swell in the Wave Pool.
There’s the man-made beach at Recreation Lagoon with nets to keep any stingers at bay. There’s Lake Alexander in the East Point Reserve and Leanyer Water Park with its two swimming pools and water playground that include three massive waterslides. You can even swim at Crocosaurus Cove by hopping in the Cage of Death! And it’s not far to Berry Springs Nature Park and Litchfield Natural Park for clear pools, creeks and waterfalls.