This is a great summer area. Not only is it nice and cool because its at the top, but it is also in the shade for a good portion of the day. You are unlikely to see many other people here, and if you do it is likely they are hiking out to the Fortress and not stopping to climb the few routes that are here. If you've not climbed up this high on Mt. Lemmon you will be surprised to see that the rock is different. It is very much like the rock in Tuolomne Meadows in YNP. You can toprope most of these climbs by accessign the top of the cliff. This area is affected by the Pergrine Falcon closure that applies to the other summit crags.
Getting There
Drive all the way past the ski area and up the access road to the Mt. Lemmon Observatory. There is a parking lot with trailhead that heads out to Lemmon Rock Lookout. Hike this very wide trail for a ways past Quartzite Spring (metal shed). Further down you will see a electrical transformer box on the right. Shortly after this cut left into the pines and pick up a very distinct trail that leads to the back of the Ravens and The Murray Wall.
The Classics
Mountain Project's determination of some of the classic, most popular, highest rated routes for The Murray Wall:
To get to the routes on the backside, take the faint trail down and around a large fallen tree then work back toward the cliff. Scramble through a notch and up to the climbs on the left wall.
There are actually several more easy routes on the backside of the Murray wall. These can be found in EFR's squeezing the lemmon II. All of them are slab climbs on crystals.