Siṃhala Dvīpa is a great island in the ocean. King Bṛhadratha rules it. Padmāvatī, an avatāra of Lakshmīdevī and the future wife of Bhagavān Kalki, was born in his royal house. The Kalki Purāṇa describes the island as rich, beautiful and holy, with people of all four varṇas living in it.

Chosen as the birthplace of Lakshmīdevī

Bhagavān Vishṇu spoke to the devas at Goloka and promised to come down as Kalki. He said: “Padmā, the avatāra of Lakshmīdevī, will be born in Siṃhala Dvīpa as the daughter of King Bṛhadratha and Queen Kaumudī, with lotus-like eyes.” So Bhagavān Vishṇu himself named Siṃhala Dvīpa as the place where his consort would be born in the Kali age. From this island she would be united with the last avatāra. This is told in the Kalki Purāṇa, Prathamāṃśa, Chapter 1.

The island

The Kalki Purāṇa, Prathamāṃśa, Chapter 4, describes the island in rich detail.

Buildings. There were great palaces (prāsāda) and fine mansions (harmya). Crystal walls were decorated with paintings, and golden light shone everywhere.
Water. The lakes were tinged crimson by the reflection of red lotuses. They were full of swans, ducks (kāraṇḍava) and other water birds. The scent of lotus honey hung thick in the air, and bees drunk on nectar hummed all the time.
Gardens. Large groves and garden parks (udyānavana and upavana) spread across the island.
People. All four varṇas lived there. They were prosperous and followed their own dharma. The people were handsome and well dressed, and they bore auspicious marks.

The king and queen

King Bṛhadratha ruled Siṃhala Dvīpa. The Kalki Purāṇa, Prathamāṃśa, Chapter 4, calls him mahāsainya (one with great armies) and a brave, powerful ruler. His queen was Kaumudī. The kingdom was prosperous and well governed.

The svayaṃvara of Padmāvatī

Padmāvatī’s svayaṃvara (the ceremony in which a princess chooses her husband) took place on Siṃhala Dvīpa. Kings from all the kingdoms of the earth came to the island. They came on horses, elephants and chariots, with armies and banners. The svayaṃvara hall was magnificent.

Then Padmāvatī entered the maṇḍapa. Every king who was gathered there saw her and was turned into a woman. This showed that Bhagavān Śiva’s boon was complete and that only Nārāyaṇa was worthy of Padmāvatī. The Kalki Purāṇa tells this in the Prathamāṃśa, Chapter 5.

Connection to Kalki’s mission

The Śuka, Kalki’s divine parrot, flew across the ocean to Siṃhala Dvīpa more than once. First he went to see the island and report to Bhagavān Kalki. Later he went as Bhagavān Kalki’s own messenger to Padmāvatī. In the Prathamāṃśa the island is the place toward which Bhagavān Kalki’s mission is turned, while he waits for the day of the union.

Paraśurāma had already named Siṃhala Dvīpa and Padmāvatī when he spoke to Bhagavān Kalki: “From the devī Kamala (Padmā), who has lotus-like eyes and who has come down in Siṃhala Dvīpa, you will receive your priyapatnī (dear wife).” This is in the Prathamāṃśa, Chapter 3.

Sources

Kalki Purāṇa, Prathamāṃśa, Chapters 1, 3, 4, 5 and 6