Sanskrit
अव्यक्तोऽक्षर इत्युक्तस्तमाहुः परमां गतिम् । यं प्राप्य न निवर्तन्ते तद्धाम परमं मम ॥
avyakto'kṣara ity uktas tam āhuḥ paramāṃ gatim yaṃ prāpya na nivartante tad dhāma paramaṃ mama
Translation
That unmanifested, "the Indestructible," It is called; It is named the highest Path. They who reach It return not. That is My supreme abode.
Annie Besant · The Bhagavad-Gita, translated by Annie Besant (4th ed., 1922) — Wikisource · Public Domain
Explanation
The higher unmanifest introduced in verse 20 is now named directly: akshara, the indestructible — the same word used to define brahman back in verse 3. It’s called the highest path and Krishna’s own supreme abode, and reaching it means no return, which finally answers in full the question verses 15-16 opened about what lies beyond even Brahma’s realm.