Valmiki Ramayana Kishkindha Kanda Sarga 50 Shloka 10
Original Shlokaततस्तद्बिलमासाद्य सुगन्धि दुरतिक्रमम्।।4.50.10।। विस्मयव्यग्रमनसो बभूवुर्वानरर्षभाः।
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ततः then, वानरर्षभाः bulls among monkeys, सुगन्धि fragrant, दुरतिक्रमम् difficult to enter, तत् that, बिलम् cave, आसाद्य reached, विस्मयव्यग्रमनसः bewildered, बभूवुः became.
The bulls among the monkeys were bewildered when they reached the cave which was difficult to access.