'Escape From Orthanc'

So it was that when summer waned, there came a night of moon, and Gwaihir the Windlord, swiftest of the Great Eagles, came unlooked-for to Orthanc; and he found me standing on the pinnacle. Then I spoke to him and he bore me away, before Saruman was ever aware." --Gandalf describes his imprisonment in and escape from Orthanc.