SB 4.29.80

maitreya uvāca
bhāgavata-mukhyo bhagavān
 nārado haṁsayor gatim
pradarśya hy amum āmantrya
 siddha-lokaṁ tato ’gamat
maitreyaḥ uvāca — Maitreya said; bhāgavata — of the devotees; mukhyaḥ — the chief; bhagavān — the most powerful; nāradaḥ — Nārada Muni; haṁsayoḥ — of the living entity and the Lord; gatim — constitutional position; pradarśya — having shown; hi — certainly; amum — him (the King); āmantrya — after inviting; siddha-lokam — to Siddhaloka; tataḥ — thereafter; agamat — departed.
The great sage Maitreya continued: The supreme devotee, the great saint Nārada, thus explained to King Prācīnabarhi the constitutional position of the Supreme Personality of Godhead and the living entity. After giving an invitation to the King, Nārada Muni left to return to Siddhaloka.

Siddhaloka and Brahmaloka are both within the same planetary system. Brahmaloka is understood to be the highest planet within this universe. Siddhaloka is considered to be one of the satellites of Brahmaloka. The inhabitants of Siddhaloka have all the powers of yogic mysticism. From this verse it appears that the great sage Nārada is an inhabitant of Siddhaloka, although he travels to all the planetary systems. All the residents of Siddhaloka are spacemen, and they can travel in space without mechanical help. The residents of Siddhaloka can go from one planet to another individually by virtue of their yogic perfection. After giving instructions to the great King Prācīnabarhi, Nārada Muni departed and also invited him to Siddhaloka.