Katherine

Distances don't seem so far in the Northern Territory, compared to WA that is. We crossed the boarder, and turned our clocks forward an hour and a half after we'd only been on the road for less than an hour.
We stopped for lunch at Timber Creek and were tipped off about the crocs in the river behind the caravan park. It was a beautiful deep river with pandanus palms, deep green water and a narrow bridge across it. Out on the bridge some other kids were looking for crocs when suddenly out of the green depths came a large freshie, probably about 2m long. Then another one popped up and another. They were beautiful and terrifying. I'm not sure if I'm ready to see salties.

We'd intended to stay at a roadside rest area for the night but I then realised that would mean we'd probably miss Nitmiluk (Katherine) Gorge. So we pushed on and after a quick stop for fuel and the visitors centre in Katherine we made it to the NP before dark and had time for a swim in their resort style pool.
There are no NP entry fees in the NT. Camping fees apply based on the level of services at the camp ground. This one was pretty much a caravan park so paying $47 for unpowered for the night seemed pretty normal, and that pool was the best so far. We found a very quiet spot down the back and had a good nights sleep.
While Evan packed up the camper in the morning I took the boys down to the river and up the track to the lookout over the first gorge. It was a great view and the boys got a good echo from the sandstone walls on the other side of the gorge. I think there are 5 gorges at Nitmiluk but unless you want to do some extreme hiking, go on a boat cruise or take a helicopter flight ($99 gets you 9 mins) you only really see the first gorge.
There is a huge colony of flying fox down by the river that in try flying fox style, smell and make a lot of noise. I'm sure the crocs in the river get a good feed if any of them accidentally fall.
We were much more impressed with Edith Falls on the road out of Katherine. They are at the other end of Nitmiluk. It is a large swimming hole with a waterfall across the water. I think we'll camp there on our way south again.