The Back Door is the somewhat secluded area down between the South face of the Monolith and the Reservoir/Tiburcio's X.
Although there aren't very many routes, the rock quality of the area is excellent, and the routes themselves are all quality. The route difficulty is varied, and challenging at most levels. This is a good place to check out when it gets hot. It's normally much less crowded than Discovery Wall or the Monolith, and is a great change of pace for the frequent Pinnacles visitor.
Getting There
There are various approaches detailed in the guidebook, but the most straightforward is to follow the main (Moses Springs) trail just above the East Face of the Monolith up a short ways to the reservoir. Once there, continue steeply up the trail for a short distance, passing under Tiburcio's X, until the West face of the Monolith is clearly visible. Scramble up the large boulder that borders the trail nearest the West face, and find the bolted chain anchor at the lip. Rappel here, and find yourself at the base of Auto Cream.
Another approach breaks off the Moses Springs trail where it meets the Northwest corner of the Monolith. Scramble up a gentle hill to your right at this juncture, and find yourself confronted by the imposing, lichen-covered face of The Druid. Follow the trial, passing under The Druid, and contour uphill to meet the Back Door wall. This small trail is hard to spot when the brush is thick, and the poison oak grows rampant around it in the springtime, so wear long pants- or approach in the winter.
Another more annoying approach is to trek down below the East Face routes, past Subterranean Tango and Bridwell Bolts, and then scramble up the loose hill, wending your way through boulders. This approach will put you right at the base of The Black Dagger boulder. Continue up the hill to reach the Back Door wall.
The Classics
Mountain Project's determination of some of the classic, most popular, highest rated routes for The Back Door: