The three cities (Tripura) are described in Chapter 1, Yuddha Khanda (Rudra Khanda) of Shiva Mahapurana.
Mayadanava built three different cities at one place made of gold, silver and iron & steel for Tarakaksha, Kamalaksha and Vajramali respectively.
आज्ञां ददौ मयस्यापि कुरु त्वं नगरत्रयम्।
काञ्चनं राजतं चैव अायसं
चेति भो मय! ॥ ५५॥
Mayadanava was then ordered to build three cities of gold, silver and
iron.
इत्यादिश्य मयं ब्रह्मा प्रत्यक्षं प्राविशद्दिवम्।
तेषां
तारकपुत्राणां पश्यतां निजधाम हि॥५६॥
After thus issuing a command to Mayadanava, in the presence of the
sons of Taraka, Brahma- the creator, returned to his abode, in full
view of all of them.
ततो मयश्च तपसा चक्रेत धीरः पुराण्यथ।
काञ्चनं तारकाक्षस्य
कमलाक्षस्य राजतम्॥५७॥
विद्युन्माल्यायसं चैव त्रिविधं
दुर्गमुत्तमम्।
स्वर्गे व्योम्नि च भूमौ च क्रमाज्ज्ञेयानि तानि वै॥
५८॥
Then Maya who was filled with wisdom, making all the efforts,
made the city of gold for Tarakaksa, a silver city for Kamalaksa and a
city of iron, for Vidyunmall, together with three forts, which were
located with heaven, the sky and the earth.
दत्त्वा तेभ्योऽसुरेभ्यश्च पुराणि त्रीणि वै मयः।
प्रविवेश स्वयं
तत्र हितकामपरायणः॥ ५९ ॥
Bestowing the three cities to the Danavas, keeping in view their
welfare, he himself also started living there.
एवं पुरत्रयं प्राप्य प्रविष्टास्तारकात्मजाः।
बुभुजुः सकलान्भोगान्
महाबलपराक्रमाः॥ ६०॥
After getting the possession of the three cities, the sons of Taraka,
entered therein. The immensely valorous Danavas, started enjoying all
the comforts there.
They had citadels, Rivers, kalpavriksha trees ,places for worship of Shiva.
कल्पद्रुमैश्च सङ्कीर्ण गजवाजिसमाकुलम्।
नानाप्रासादसङ्कीर्णं
मणिजालसमावृतम्॥ ६१॥
Numerous kalpavriksas were growing in those cities, besides numerous
horses and the elephants. There were several places, with gem-studded
windows.
सूर्यमण्डलसङ्काशैर्विमानैः सर्वतोमुखैः।
पद्मरागमयैश्चैव शोभितं
चन्द्रसन्निभैः॥ ६२॥
There were several planes in which rubies were fixed in all the four
sides, and illumined like the sun rays. Some of them resembled the
moon, which decorated the city.
प्रासादैर्गोपुरैर्दिव्यैः कैलासशिखरोपमैः।
दिव्यस्त्रीजनसङ्कीर्णैर्गन्धर्वैः सिद्धचारणैः॥ ६३॥
There were the huge royal places. The gates of the cities, resembled
the peaks of the Kailasa mountain. There were numerous divine damsels,
besides those of the Gandharvas, siddhas and cdranas.
रुद्रालयैः प्रतिगृहमग्निहोत्रैः प्रतिष्ठितैः।
द्विजोत्तमैः
शास्त्रविज्ञैः शिवभक्तिरतैः सदा।। ६४॥
Every house had a Siva temple, places for performing the homas, and
the learned people well-versed in the scriptures, lived there.
वापीकूपतडागैश्च दीर्घिकाभिः सुशोभितम्।
उद्यानवनवृक्षैश्च
स्वर्गच्युतगुणोत्तमैः।। ६५॥
There were enough of step-wells, wells, tanks, both big and small,
besides the divine orchards with charming trees.
नदीनदसरिन्मुख्यपुष्करै: शोभितं सदा।
सर्वकामफलाद्यैश्चानेकैर्वृक्षैर्मनोहरम्॥ ६६॥
All the rivers, rivulets and canals were filled with water. The place
was quite delightful with the trees which yielded useful fruits.
मत्तमातङ्गयूथैश्च तुरङ्गैश्च सुशोभनैः।
रथैश्च विविधाकारैः
शिबिकाभिरलङ्कृतम्॥ ६७॥
The place had the herds of elephants, horses, chariots and palanquins
of different types.
People there even studied Vedas, women were chaste and highly devoted to Lord Shiva. This is also the reason why Lord Shiva was reluctant to destroy three cities initially.
समयाध्युषितैधैव क्रीडास्थानैः पृथक्पृथक्रा वेदाध्ययनशीलाभिर्विविधाभिः
पृथक् पृथक्॥ ६८॥
During the evening time, besides the play grounds, the separate rooms
were made for the study of the Vedas.
अदृष्टमनसा वाचा पापान्वितनरै: सदा।
महात्मभिः शुभाचारैः पुण्यवद्भिः
प्रवीक्ष्यते॥६९॥
No sinful persons, could be found there who spoke evil words by speech
or the mind. Everywhere only the noble people with good conduct could
be seen.
पतिव्रताभिः सर्वत्र पावितं स्थलमुत्तमम्।
पतिसेवनशीलाभिर्विमुखाभिः
कुधर्मतः॥७०॥
The houses of the city were adored with the chaste women who were
devoted to their husbands and served them well, and were averse to
evil ways.
दैत्यशूरैर्महाभागैः सदारैः ससुतैर्द्विजैः।
श्रौतस्मार्तार्थतत्त्वज्ञैः स्वधर्मनिरतैर्युतम्॥७१॥
The immensely fortunate, daitya-warrior lived with their sons and
wives, besides the Brahmana, who were well-versed in the Smarta
doctrine and were devoted to their dharma.
व्यूढोरस्कैवृषस्कन्धै: सामयुद्धधरै: सदा।
प्रशान्तैः कुपितैश्चैव
कुब्जैर्वामनकैस्तथा॥७२॥
There were enough of dwarfs, having broad chests, high shoulders,
well-versed in peace and war, who could get enraged at the appropriate
time only and found everywhere.
नीलोत्पलदलप्रख्यैर्नलकुख्रितमूद्धजै:।
मयेन रक्षितैः सर्वैः
शिक्षितैर्युद्धलालसैः॥७३॥
Mayadanava, had kept on duty the warriors there, who had the
complexion like the blue lotus flowers, having the curly hair
resembling the black wasps and who were always anxious to fight.
This is mythological description or mythological story of Tripura Dahana. But three cities or Tripura have deeper metaphorical meanings. Three cities can be interpreted as three states of wakefulness, dream and profound sleep and destruction of cities is destruction of these states and dissolving into Lord, as stated in Kaivalya Upanishad (translated by Swami Madhavananda)
स एव मायापरिमोहितात्मा शरीरमास्थाय करोति सर्वम् ।
स्त्र्यन्नपानादिविचित्रभोगैः स एव जाग्रत्परितृप्तिमेति ॥ १२॥
12.With his self thus deluded by Maya or ignorance, it is he who identifies himself with the body and does all sorts of things. In the
waking state it is he (the Jiva) who attains satisfaction through the
varied objects of enjoyment, such as women, food, drink, etc.
स्वप्ने स जीवः सुखदुःखभोक्ता स्वमायया कल्पितजीवलोके ।
सुषुप्तिकाले सकले विलीने तमोऽभिभूतः सुखरूपमेति ॥ १३॥
13.In the dream-state that Jiva feels pleasure and pain in a sphere of existence created by his own Maya or ignorance. During the state of
profound sleep, when everything is dissolved (into their causal
state), he is overpowered by Tams or non-manifestation and comes to
exist in his form of Bliss.
पुनश्च जन्मान्तरकर्मयोगात्स एव जीवः स्वपिति प्रबुद्धः ।
पुरत्रये क्रीडति यश्च जीवस्ततस्तु जातं सकलं विचित्रम् ।
आधारमानन्दमखण्डबोधं यस्मिँल्लयं याति पुरत्रयं च ॥ १४॥
14.Again, through his connection with deeds done in previous births, that very Jiva returns to the dream-state, or the waking state. The
being who sports in the three cities (viz., the states of
wakefulness, dream and profound sleep) – from Him has sprung up all
diversity. He is the substratum, the bliss, the indivisible
Consciousness, in whom the three cities dissolve themselves.