Mahaulepu is usually referred to as a beach, but it is really the name for a whole area considered very sacred by the Hawaiians, both for historical and spiritual reasons.
Access to it has changed fairly recently, and so have the directions for getting there. Now you have to head south to Poipu Road all the way past the Hyatt and even after it turns into a rough dirt road. Keep going until you reach a "T" (the way ahead is blocked by a closed gate) and turn right. You are now on private land owned by the McBride Plantation and access is strictly up to them. You will shortly come to another gate with a shack on the other side of it. Normally the gate is open from about 7am to 7pm, but check the sign for any changes. There may or may not be a guard at the shack. If so, you will have to sign a liability waiver. If not, just drive on until you come to a sandy parking area. From here you take a path to the right that takes you to a gorgeous, almost always sparsely-populated beach called Kawailoa. Walk westward (to your right facing the ocean) past the only private home allowed in the area, until you come to the stream pictured above (ocean conditions may alter the reality).
Wade the shallow stream and head for the sandy path you can see on the far side. On the right where the sandy path begins, look for a faint trail on the right that follows the stream inland.