Went to the Lagoon which is situated on the Darwin waterfront precint. This is water from the harbour netted off as to not allow any nasties in. You get a few little fish and sea weed which the life guard is scooping out constantly. It costs nothing. My kids had a ball as it's the closest they have been to having a beach experience for a long time. I was a bit put off by the seaweed at first but if you walk around a bit further it clears up. It is very salty water which sounds weird but it really is although I believe it would be quite healing to the skin. There is a few shelters to sit under and some bench seats. Plus plenty of eateries not to mention Trampoline ice creamery. Park at the underground parking just alongside Vibe hotel which is free for first two hours then $2 an hour after that. Which is very cheap.