Ramayana
अयं खलु सुदुर्गम्यः प्रेतराजपुरं प्रति । मार्गो गच्छति दुर्धर्षो यमस्यामित्रकर्शन ॥ 7-20-21 ॥
"This road, O tormentor of foes, is very hard to traverse and difficult to assail; it leads toward the city of Yama, the king of the dead."
english translation