Canto 3 -
Araṇya-kāṇḍa
Chapter 73: Kabandha Requests Śrī Rāma to Visit Śabarī
Text 3.73.39
राम तस्य तु शैलस्य महती शोभते गुहा।
शिलापिधाना काकुत्स्थ दुःखं चास्याः प्रवेशनम्॥
rāma tasya tu śailasya mahatī śobhate guhā
śilāpidhānā kākutstha duḥkhaṁ cāsyāḥ praveśanam
rāma = Rāma; tasya tu = that; śailasya = in mountain; mahatī = a large; śobhate = is beautiful; guhā = cave; śilā-apidhānā = it is covered by a rock; kākutstha = O descendant of Kakutstha; duḥkham = it is difficult; ca = and; asyāḥ = into it; praveśanam = to enter.
Rāma, a large cave in that mountain is beautiful. O descendant of Kakutstha, it is covered by a rock and it is difficult to enter into it.
It is difficult to enter into it because it is at a high altitude.