A porta inferi....

...Facilis descensus Averno.
Noctes atque dies patet atri janua Ditis:
Sed revocare gradum, superasque evadere ad auras,
Hoc opus, hic labor est.

-Virgil

And Dryden's translation:

The gates of Hell are open night and day,
Smooth the descent, and easy is the way;
But to return, and view the cheerful skies,
In this, the mighty task and labor lies.