Colca Canyon is the most popular place to watch condors. The canyon is 3400 m deep, which is more than two miles. Standing on the rim, on a good day you will see several condor soaring on the thermals that rise out of the canyon. If you’re lucky, they will come close enough for you to see their eyes without binoculars.
Most people go to Colca Canyon from Arequipa. Many tour agencies in Arequipa offer multiday tours or treks into Colca Canyon.