from Darwin to Darwin in 3 weeks with a rented car

In theory it's possible, however note the following:

• it is a very long haul to Broome and back by road and I'm not sure you'll find the rewards sufficient (without travelling the Gibb River Road)
• you cannot do a triangle - certainly not in a rental car - you need to drive 1,200 km from Alice Springs back up the Stuart Highway, and turn west at Katherine, to stay on the bitumen
• similarly, you would have to do a very long back-track from Broome to Darwin via Hwy 1 and Katherine again
• also note that September is starting to get hot and humid in the north away from the coast (Kakadu NP and Hwy 1 from KNX to Broome and back)

Therefore I suggest you consider:

• see Darwin / Kakadu NP / Litchfield NP / Mataranka, etc
• drive to Yulara (overnight) see Uluru, Kata Tjuta, and of course Kings Canyon (overnight)
• drive the West McDonnell's to Glen Helen Gorge and overnight (outstanding trip)
• see around Alice Springs (2-3 nights - fascinating place)
• drive back to Katherine only as far as Kununurra - and visit Lake Argyle, El Questro resort farm, and the beautiful Purnululu NP (Bungle Bungles)

I think that is a very good three weeks indeed ... but don't leave the Top End until too late into September. Take a few days to enjoy Darwin itself as well.

I agree with Ian, the drive would involve a lot of backtracking along the same roads. There is no paved road from Alice Springs to Broome. I just looked on google maps and its very misleading as the Tanami Road looks to be a viable option, but really isn't with a hire car. Google it and you will see its a dirt road.

Thx alot for your advices
Yes you are right too many back tracking
I think I will consider 2 or 3 possibilities
1. Darwin Alice spring ayers rock and back to Darwin by car
2. Arrive in Cairns stay a couple of days then fly to Alice spring . rent a car there for a week and then fly to Darwin and rent again a car for an other week.
Wich options would you recommend best
Is the road from Darwin to alice spring interesting or is it just a long straight without too much to see
Thx for your answer
Olilux

Is the road from Darwin to alice spring interesting or is it just a long straight without too much to see

A few things on the way worth seeing like the Devils Marbles, also stop for a day or two in Katherine to see the gorge. A few things in and around Katherine, plus then you can do Litchfield and/or Kakadu NP's before getting to Darwin.

Arrive in Cairns stay a couple of days then fly to Alice spring . rent a car there for a week and then fly to Darwin and rent again a car for an other week.

I think this is a very good option ... the main downside is that flights Cairns > Alice and Alice > Darwin are generally not very cheap (so little competition). However if the experience is more important than saving a few hundred dollars, then what you are planning to do here is by far the best.

A week around the Centre and a week around the Top End is very good indeed. And you save another week for more North Queensland maybe - add days for Townsville / Magnetic Island, in Port Douglas, the Daintree Rainforest, and the Reef.

really between katherine and devils marbles its 500km of SFA, and same again devils marbles (aka rainbow serpents eggs) to alice springs..

its a more interesting road the direct tanami road from alice springs to halls creek. but after the first 300 kilometers it becomes quite corrugated dirt road, for the next 700 km or so, quite a good chance it could shake an exhaust system off a hire car, would be alot of explaining to do ..

i quite like this road though, its one of the most remote main roads in the country, and a definite short cut, saves 1000km

Hallo Thx to all of you for your kind advices.
I have one more question coming from a different idea and avoiding to fly inside Australia
Do you advice to make the trip from Adelaide and drive up to Darwin via alice spring and katherine giving the car back in Darwin
What is the drop off i would pay as I have read that the drop off is quite high in Australia.
An othe idea is to take the car in Adelaide and driving up to Broome via alice and Katherive, leaving the car in Broome and then flying from Broome to darwin
Which of the 2 solutions would be the best giving teh fact that I woul have around 15 days in Australia

thx for your answer
BR
Olilux

Given you have only 15 days in Australia, why do you wish to avoid internal flights ... the fares (plus local rental cars in Alice and Darwin) would be considerably cheaper in both time and money that the very long drives you are suggesting. I especially believe that the drive to Broome via the highway is not really rewarded enough.

So would you avoid flying from side of Europe to the other? Australia is bigger than europe in many ways, with far less in between the towns than in Europe. You are trying to do far too much in 15 days. Yes the drive from Adelaide to Darwin in around 15 days is about right to see central Australia and Kakadu.

Don't try and get to Broome. I'm guessing you've seen the camel ride on the beach photos and now want to go there, but really there is not much in Broome.

Yes drop off is high in Australia because you've just crossed an entire continent to drop the car off. I imagine if you hired a car in Spain and dropped it off in Hungary the fees would be high too.