The Hiline Trail is one of most challenging mountain biking trails in Sedona, and it includes substantial climbs and highly technical singletrack with some significant exposure. That said, the riding is exciting and always scenic. Plently of people hike this trail for its magnificent views of Cathedral Rock, so if the riding becomes too technical and you hike-a-bike a few sections, you'll still be glad you came.
To find the trail, park in the Yavapai Point parking lot off of Hwy 179. Make sure to use the pay machine to get a parking pass; it is located toward the middle of the loop where you park and costs $5 for one day. After parking, go back toward the Hwy 179 and take a right on easy, mostly flat Coconino Trail. There are some nice cacti and other vegetation along the trail if views of the amazing red rock against the beautiful blue sky aren't not enough. Take a right on the Slim Shady Trail, which is mostly easy apart from a few big rocks.
Stay on this trail for a short distance before you take a left on Hiline, and then get ready to climb. This climb is no joke, especially if you are not used to the high elevation. Bring lots of water and a snack or two. This climb is very technical: Huge rocks block the path, and there are multiple areas of extreme exposure. Take your time and make sure that if you fall you fall away from the cliff.
Once you make your way to the top, enjoy the view. This is the most beautiful part of the ride. Drink some water and take a snack break. The next section of Hiline is mostly downhill riding on flat red slick rock. Toward the end of Hiline there is a section with a warning that you are entering a double black diamond section. Take this warning seriously, because the next section is steep, slick, and extremely technical. Walk what you don't feel comfortable riding.
After you have successfully completed Hiline, take a right on the Baldwin Trail. This trail is much easier than Hiline. There are ups and downs and all-around fun. Next take a right on Templeton Trail. This trail is a bit more technical and mostly up hill. It goes by Oak Creek and is highly trafficked by hikers. Take a break by the creek because you are about to climb again. This section is sandy, and it can be hard to get a good flow because there are so many hikers. This trail also goes by the entrance to Chapel Rock, where you can visit the vortex if you have the energy to climb the natural staircase. After climbing Templeton, take a right on Slim Shady Trail, which is nice and flowy with a few tough rocky sections. Then take a left on Kaibab Trail, a mostly downhill and flowy trail that ends at the Yavapai Point parking lot. Pat yourself on the back because you just rode Hiline, one of the hardest trails in Sedona, and you made it back after over 7 miles of beautiful, classic Arizona singletrack.