"into a Slough of Despond"
by cm

Pilgrim's Progress
Public DomainPilgrim's Progress - Credit: Joseph Edgar Boehm
The Slough of Despond was a bog in John Bunyan's The Pilgrim's Progress, into which the hero Christian sinks under the weight of his sins and guilt.  It was supposedly inspired by a real place near Bunyan's cottage in Harrowden, known at the time as Squitch Fen.