Ephedra's Grotto, also called Medieval Chamber, is one of the most-traveled slot canyons in the Moab area because of its popularity with commercial guides. It is a relatively short canyon with two spectacular rappels, one of which drops through a natural rock arch reminiscent of those in Arches National Park. Any number of outfitters in Moab offer this as a half-day trip, but you can do it on your own if you have the technical expertise and equipment for 100-foot rappels.
This canyon is within Sand Flats Recreation Area just outside of Moab. Begin from the radio tower road 2.1 miles beyond the entrance station. Your car shuttle will need to be set at the Negro Bill Canyon Trailhead along Highway 128.
Walk past the gate and along the road. Shortly after passing the tower, take the four-wheel drive road to the left and follow the network of footpaths into a wash, heading northeast. You may link up with another four-wheel drive road for part of this hike. Eventually the rock fins will close in on miniature narrows. There are actually two forks at the head of this canyon that lead to two separate rappels. If you head too far north along the second four-wheel drive road you will be at the shorter and less exciting of the two, though this is the route preferred by some of the commercial guides because it is easier. The rappel here is not as long and does not enter the Medieval Chamber proper, but it still leads to the arch rappel. If you find yourself at this shorter rappel, which drops into a widening chimney, you can easily cross up and over the slickrock dome to the south and access the other rappel instead.
If you are entering via the south fork of the canyon you will walk through a walled-in sandy wash. There is one dryfall that presents a tricky downclimb into a possible pool, and there are a few others that require a short downclimb or jump down. This wash is dry most of the year, but in spring or after heavy rains the pools my linger.
Soon you will come upon the entrance to the Medieval Chamber, a wide shaft that drops suddenly away through the canyon floor. This is a 100-foot rappel off a three-bolt anchor. There is one pool midway down that you will wade through before the second stage of the rappel. Observe the interplay of light and dark in the bottom of this chamber, and enjoy the cool shade. Pass through a narrow slot and emerge into another wide section of the canyon.
This next rappel is even more spectacular. From an established anchor on a sturdy tree, descend a free-hanging 100 feet through the 200-foot span of Morning Glory Arch. Be careful not to throw ropes off the top here, because hikers may be on the trail below. Once on the canyon floor, pack up your ropes and begin the scenic hike down Negro Bill Canyon to the Colorado River. This hike requires crossing the ankle-deep stream a few times, and there are several inviting pools in which to cool off on a hot day.