Srimad-Bhagavatam: Canto 4 - Chapter 1 - Verse 15
मन्यमान इदं विश्वं मायारचितमात्मनि ।अविद्यारचितस्वप्नगन्धर्वनगरोपमम् ॥ १५ ॥
manyamāna idaṁ viśvaṁmāyā-racitam ātmaniavidyā-racita-svapna-gandharva-nagaropamam
Śrīla Dhruva Mahārāja realized that this cosmic manifestation bewilders living entities like a dream or phantasmagoria because it is a creation of the illusory, external energy of the Supreme Lord.
In the deep forest it sometimes appears that there are big palaces and nice cities. That is technically called gandharva-nagara. Similarly, in dreams also we create many false things out of imagination. A self-realized person, or a devotee, knows well that this material cosmic manifestation is a temporary, illusory representation appearing to be truth. It is like a phantasmagoria. But behind this shadow creation there is reality — the spiritual world. A devotee is interested in the spiritual world, not its shadow. Since he has realization of the supreme truth, a devotee is not interested in this temporary shadow of truth. This is confirmed in the Bhagavad-gītā (paraṁ dṛṣṭvā nivartate).