Nilgiri or the “Blue Mountain” in Purusottama Kshetra was the abode of Lord Nilamadhava [Purusottama], a divine form of Lord Vishnu. The first Sri Jagannath Temple is believed to have been built on this mountain. The age of Nilgiri is unimaginable.
It existed even before the Satya Yuga and the secret of this place was first revealed to Lord Brahma. Later on, during the time of Treta Yuga, when Lord Rama, the incarnation of Lord Vishnu decided to perform Ashwamedha Yagna, Nilgiri again came into the picture.
When the Yagna horse, according to the rules of the Yagna, was let lose, Shatrughna, the youngest brother of Lord Rama, was assigned to the task of following and protecting the animal until it returned to the site where the Yagna was to be performed. It was during this pursuit that he chanced to see Nilgiri.
When he caught sight of the hill, Sumati, his minister was with him and Shatrughna wanted to know from him about the hill which was shining like silver. In reply, Sumati said that it was Nilgiri [Blue Mountain] and explained to him the reason behind the glorious luster it had. He said that the shine was coming from the surrounding hills, the summits of which were heaps of crystals and other jewels. He also said that the hill always remained invisible to sinners.
People, who do not trust in the omnipotence of Lord Vishnu, do not obey the rules mentioned in the scriptures written by great saints and take decisions based only on their logic and intelligence cannot see it. Nor can the ones who offend hungry guests, betray others and do not like songs of the glory of Lord Vishnu. He, who climbs the hill and bows to the Lord Purusottama and worships him, gets transformed into the four-handed form of the Lord.
While saying this, Sumati had noticed that the horse was already at the foothill; so he urged upon Shatrughna to go up the hill and bow to Lord Purusottama. He also added that Rama, in fact, was the manifestation of Lord Purusottama and his wife Sita of Goddess Mahalaxmi.
In the meanwhile the horse had already gone up the hill and Shatrughna followed the horse and reached there too. He had a bath in the holy water of Ganga Sagar and bowed to Lord Purusottama. He sang the glory of the Lord and experienced a sense of fulfillment.