Hiking is a good way to see more of Lahaina, as there are lots of trails in the area.  For a relatively easy hike, walk to see the petroglyphs that are carved into lava rock about an hour's hike from the Olowalu General Store, or up to the "L" (for Lahaina) outlined on the side of Mount Ball behind the high school.   More adventurous hikers might continue on up the hill from the "L" to the grave of David Malo, a renowned Hawaiian author and historian who wrote Hawaiian Antiquities, an account of ancient Hawaiian culture

If you'd rather get off the beaten path and into the water, there are several scuba diving and snorkeling tour companies in the area, like Lahaina Divers  or Pacific Dive , which offers a trip called Gorilla Dive for a more rigorous extreme diving experience.  Also, some tour companies will accommodate requests for custom dive packages, so it's sometimes possible to go to places other tourists don't normally get to dive. 

One thing to do that will take you away from the usual tourist activity are the Maui Stables, a three hour guided trip on horseback in the beautiful town of Kipahulu. The ranch is owned by the very same guys who were raised as children playing at the top of  the mountain ranges.  They not only know the native Hawaiian language, but they know every fruit, tree, animal, and leaf, as well as the legends that accompany it. They recommend 2 1/2 hours to reach Maui Stables from Lahaina, but 3 1/2 hours would allow you to really enjoy the breathtaking views along the route. Your drive will take you approx 20 miles or so on a semi-smooth dirt road, thinking you have gone in the wrong direction. You will traverse cliffs, encounter seaspray while following the mile markers. You don't need a four wheel drive vehicle, but it is highly recommended to go in the morning as you don't want to drive this road at night. It will also help to have a good driver and full tank of gas.  There is no cell phone reception, unless it's with Nextel. If you get stuck, eventually someone will drive past you. It's a good feeling to see someone else on this desolate road. Believe it or not, according to the guys, they receive mail 5 days a week!

The ride is not recommended for small children They take very good care of their horses and the 'outhouse' for those you with restroom issues is, surprisingly, quite fancy.  Flush toilet, granite marble top, etc. They provide snacks prior to the ride, give a short lesson and nice sandwich lunch afterwards. Make sure you wear long pants,  tennis shoes and lots of sunscreen.  A bit pricey, but well worth every single penny.

An idea for a great trip would be to leave Lahaina, go horseback riding at Maui Stables, drive out the other end towards Hana, spend one night there, then continue out of Hana onto the bumpy road on the next day. It's unbelieveable that there is actually life on this side of the island as it is so isolated.

Another great way to find ways to get off the beaten path in Lahaina is to ask the locals about the area.  Hotel staff, waiters, gift shop clerks are usually more than happy to point you to some great out-of-the-way places that can't be found in any of the guidebooks.