Facilis descensus Averno; Noctes atque dies patet atri janua Ditis; Sed revocare gradum, superasque evadere ad auras, Hoc opus, hic labor est.
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 task and mighty labor lies.
Virgil, Æneid (29-19 BC), VI. 126, as translated by John Dryden. ("Averni" in some editions.)
Variant translation: Easy is the descent to Lake Avernus (mouth of Hades); night and day the gate of gloomy Dis (god of Hades) is open; but to retrace one's steps, and escape to the upper air, this indeed is a task; this indeed is a toil.