Drive west on highway 30
There are a lot of things to do at Maui. Almost everywhere you go they are going to offer you tours. There are also a lot of places that advertise low price tours, but as usual there is a catch. In order for you to get the low price you have to attend a time-share presentation or commit to something.
One of the best things to do in Maui is just to drive west on the highway 30 and stop in different places. I have to warn you. There is no really signs on the road for these places, but you will see around the highway some cars stopped at the side of the road, and my advice is to stop there to look around and you will discover great beautiful places.
Going west, drive until the highway it is not a highway anymore but becomes a road. It is around mile 43. Turn around and drive back stop when you see cars on the side of the road. The first think you can find, around mile 42 ½ is the Olivine pools. Something that most books will not tell you is that most attractions are not just some steps from where you park. Most of them require you to climb down and up on rocks. So please take some tennis shoes or water shoes. Flip flops will be slippery. It is quite an exercise, so take water with you too.
Keep driving and you will also find the Nakalele Blowhole. Once again you have to go down around 1000 feet (on rocks) but once you get down, the experience is unique. There are times the blowhole is not blowing, but stick around, because sooner or later it will be.
You will also see beautiful bays and beaches so stop to enjoy the calm water and even some snorkeling.
Take water and snacks with you as the road does not have stores or restaurants. Also make sure you have gas on your car.
The drive with stops will take around 4 to 5 hours, which will give you time to schedule a nice dinner at Lahaina.