Nīlācala, the “Blue Hill”, is the sacred hill at Purushottama Kshetra on the eastern shore of Bhārata. The great prāsāda (temple palace) of Bhagavān Jagannātha stands on it. The Skanda Mahā Purāṇa says that Nīlācala is the śarīra (body) of Bhagavān Vishṇu himself. The whole hill is Bhagavān Vishṇu, and the prāsāda at its top is his innermost home.

Bhagavān Narasiṃha in his ugra (terrifying) form is also enshrined on the hill. The blue colour (nīla) of the hill is the colour of Bhagavān Jagannātha’s own body. It is the same dark blue as the form of Jagannātha and of the earlier Nīla Mādhava.

Names

The Purāṇa gives the hill several names:

Nīlācala and Nīlādri: the blue hill (nīla is blue, acala and adri mean mountain).
Nīlagiri: the blue mountain.
Śrī Nīlācala: the same name with the honour Śrī, which shows its divine nature.

The blue of the name is the blue of Bhagavān Jagannātha’s own colour. It is the nīla of Jagannātha, the nīla of the earlier Nīla Mādhava, and the nīla of the ocean that surrounds the kshetra. (Skanda Mahā Purāṇa, Vaishṇava Khaṇḍa, Purushottama Kshetra Māhātmya, Chapter 1)

The body of Bhagavān Vishṇu

The Purāṇa says that Nīlācala is not only the place where Bhagavān Vishṇu lives. It is his own body. The hill is the body of Bhagavān Vishṇu, the prāsāda at its top is his heart, and the whole of Purushottama Kshetra is his wider form. So to set foot on the hill, to touch its earth, or to see it from far away is itself a form of darśana (sight) of Bhagavān Vishṇu. (Chapters 1, 4, 15)

The prāsāda

King Indradyumna built the great prāsāda at the top of Nīlācala. He built it to house the four dāru mūrtis (wooden images): Jagannātha, Balabhadra, Subhadrā and Sudarśana. They came out of the divine tree trunk. Brahmā himself came down from Satyaloka to do the pratishṭhā (installation) in this prāsāda. Bhagavān Jagannātha said that even if the prāsāda falls to ruin, he will never leave Nīlācala. (Chapters 18–29)

Bhagavān Narasiṃha on Nīlācala

Bhagavān Narasiṃha in his ugra form is enshrined on Nīlācala. During the pratishṭhā rites, Brahmā meditated on the Narasiṃha mahāmantra. Then the cosmic form of Bhagavān Narasiṃha appeared and filled all directions with blazing light. The ugra Narasiṃha shrine on the hill is the protecting guardian of the kshetra and of the dāru mūrtis. (Chapter 28)

Sacred geography

The hill rises from the coastal plain of the Utkala region. Within the kshetra that holds Nīlācala:

The great ocean, called Tīrtharāja, lies at the foot of the hill and reaches five krośas (a distance measure) into the sea.
The Indradyumna Sarovara (lake) lies south of the hill, near the Narasiṃha kshetra.
Eight śaktis and eight Śiva-liṅgas form a protecting maṇḍala (circle) around the hill.
Vimalā Devī is enshrined within the prāsāda grounds on the hill.

The Purāṇa says that the kshetra reaches ten yojanas (a distance measure) on the hill, here called Nīlagiri, and that a kalpa-vṛksha (wish-fulfilling tree) stands within it. (Chapter 1)

The yearly departure and return

During the Guṇḍicā Yātrā (also called the Ratha Yātrā), Bhagavān Jagannātha leaves Nīlācala for nine days. He stays at the Guṇḍicā Maṇḍapa, near the Indradyumna Sarovara. On the ninth day he comes back, facing south (the dakshiṇābhimukha return). This return is called the Sampūrṇa Yātrā, when Bhagavān Jagannātha goes back to his prāsāda on Nīlācala.

The leaving and the return are the great drama of the hill: Bhagavān Jagannātha leaves his own body, Nīlācala, for a time and then returns to live in it again. (Chapters 33, 35)

Sources

Skanda Mahā Purāṇa, Vaishṇava Khaṇḍa, Purushottama Kshetra Māhātmya, Chapters 1, 4, 15, 18–29, 28, 33, 35