The places such as atala, sutala, patala Are they different dimensions on earth? or are they different planets below earth?
The seven holes or Vivara which are under the earth Namely Atala , Vitala , Sutala ,Talatala ,Mahatala ,Rasatala and patala ,which are also called Lokas or planetary systems are described inShreemad Bhagvat purana .(see page . 755-766)
According to Purana they are below the earth and beneath each other in distance of 10,000 Yojanas. And are having same width and breadth.
उपवर्णितं भूमेर्यथासन्निवेशावस्थानमवनेरप्यधस्तात् सप्त भूविवरा एकैकशो
योजनायुतान्तरेणायामविस्तारेणोपकॢप्ता अतलं वितलं सुतलं तलातलं
महातलं रसातलं पातालमिति ॥ SB 5.24.7 ॥
upavarṇitaḿ bhūmer yathā-sanniveśāvasthānam avaner apy adhastāt sapta bhū-vivarā ekaikaśo yojanāyutāntareṇāyāma-vistāreṇopakḷptā atalaḿ vitalaḿ sutalaḿ talātalaḿ mahātalaḿ rasātalaḿ pātālam iti
Below the earth there are seven subterranean regions ,each at distance of ten thousand Yojanas in length and breadth (their name are) Atala , vitala ,Sutala , talatala mahatala ,Rasatala and patala
Bhagvat Purana is also equating these places as equal to Swarga. I.e. Bila Swarga.
एतेषु हि बिलस्वर्गेषु स्वर्गादप्यधिककामभोगैश्वर्यानन्दभूतिविभूतिभिः | |SB 5.24.8||
eteṣu hi bila-svargeṣu svargād apy adhika-kāma-bhogaiśvaryānanda-bhūti-vibhūtibhiḥ
In these subterranean regions are veritable heavens.
So they basically the lokas or abode of demons which are equal to Swarag in material things. These are not separate planets as they are said to be under the earth. And they are subterranean regions.
They are different levels or piece of land one beneath the other. Many people have accidentally found entrances to these levels, some entered and returned, some didn't. But they surely exist and can be reached through labyrinth of tunnels spread all around the world. That's all info I can provide for now...