Valmiki Ramayana Sundara Kanda Sarga 12 Shloka 17

तस्मिन् in that, रावणान्तःपुरे in Ravana's inner chambers, सः कपिः monkey, यम् where, न जगाम did not go, सः he, अवकाशः scope, चतुरङ्गुलमात्रोऽपि even four fingers of space, न not विद्यते leaving.

Even a space of four fingers in the inner chambers of Ravana was not left out in his search for Sita.