Valmiki Ramayana Yuddha Kanda Sarga 4 Shloka 115

दीप्तभोगैरिव adored with the glowing hoods,भुजङ्गेः serpents, आकीर्णम् filled with hordes, वरुणालयम् abode of Varuna, महासत्त्वै: huge snakes, अवगाढम् under water, नानाशैलसमाकुलम् different kinds mountains, सुदुर्गम् very difficult, दुर्गमार्गम् difficult path, अगाधम् deep, मसुरालयम् fathomless abode of rakshasas

Filled with serpents glowing with flaming gems on hoods, the abode of Varuna (was like underworld) with huge snakes and different mountains under water is a difficult path inaccessible and a fathomless abode of rakshasas (vanaras thought).