Near Honolulu on Oahu, this overgrown singletrack network can be technical. Watch out for the continually damp rocks and roots. To reach the trailhead from Honolulu on H1, follow Keeaumoku Street. Proceed north on Wilder Avenue and turn onto Makiki Heights Drive. Turn right onto Tantalus Drive and park at Triangle Park. CAUTION: This trail complex has been closed to mountain bikes since 1996.
Here are some notes on adventuring in Hawaii. First, unlike mainland forests, the tropical island forests can grow very dense and can mask dropoffs. Plus, the trails can be very wet and slick most of the year (December to February is the main rainy season, but expect rain all year round). Stay on the trail to avoid disorientation. Second, speaking of disorientation, be aware that most Hawaiian topographic maps use the Old Hawaiian Datum. When trying to use the latitude/longitude from those maps with a GPS unit, you will think you are 0.4 miles south/southeast of where you really are. Kind of important in a dense jungle. Third, the bacteria Leptospirosis is found in the local waters and mud. It causes flu like symptoms within 2-20 days of contact, and can be fatal if not treated with antibiotics. Fourth, when hiking about, walking sticks can be very helpful for stablity in the slick conditions, for probing mud hole depths and clearing webs of the tiny crab spider.
Overall, Tantalus / Manoa / Makiki Trail Complex is the 4th most popular mountain bike trail of all 22 mountain biking rides in Hawaii.