The south (Kaupo) coast of Maui is an alternate universe removed from the long run of resort strips on the entire west coast of the island. The arid slopes of Haleakala rise abruptly from a rugged coast that is totally undeveloped yet accessible. You won't find sand beaches, but Nu'u Bay serves up good snorkeling and petroglyphs that tell the story of inhabitants from centuries past.
The Kaupo Trail is the backdoor into the National Park, a ball-busting climb through pasturelands and native forests that finally reaches the vast red crater that is out of this world (not unlike its sister volcano to the south, Mauna Loa on the Big Island, where habitat studies today are preparing humans to go to Mars in the near future).
Huialoha Church sits on a cove facing a wild sea, one of the most serene and beautiful spots in Hawaii. Built in 1859, the church was hit by vandals in recent years, but dedicated locals have restored the interior, adding hardwood floors to this place of worship.
The center of this alternate universe is the Kaupo Store, open 24/7, except when it's not, a policy that dates from 1925. Grab an ice cream, bag of chips, or cold drink and watch the world not go by.
Only a few miles away is St. Joseph Church, erected in 1862, when there were enough people around to fill the place on Sundays. Maui Trailblazer has five trailhead sections devoted to this wild, off-beat coastline. (Hawaii the Big Island Trailblazer has details on how to visit Mauna Loa on the Big Island).