The mind is its own place.

Farewell, happy fields, where joy forever dwells!
Hail, horrors! Hail infernal world!
An thou, profoundest Hell,
receive thy new possessor
-one who brings a mind not to be changed by place or time.
The mind is its own place,
and itself can make a Heaven of Hell,
and a Hell of Heaven.

Paradise Lost, John Milton.