The mind is its own place, and in it self
Can make a Heav'n of Hell, a Hell of Heav'n.
(from a speech by Satan - lines 251-3 I think?- during the Fall, in Paradise Lost: Book I (1667) (using
http://darkwing.uoregon.edu/~rbear/lost/pl1.html
as my source); may not reflect exactly the author's own opinions in consequence, though I suspect these lines do.)