The day before the Jagannatha Puri Ratha Yatra is celebrated as Gundicha Marjana ― the cleansing of the Gundicha temple.
The day preceding the Ratha Yatra in Jagannatha Puri is Gundicha-marjana. Cleaning of the Gundicha temple takes place to welcome Lord Jagannath, Baladeva and Subhadra. The Gundicha temple is situated three kilometers northeast of the Jagannatha temple. This is where Lord Jagannatha stays for seven days at the time of the Ratha Yatra celebrations at Puri.
Sri Chaitanya Mahaprabhu would clean the Gundicha temple along with hundreds of devotees. He did this just to instruct others. Whilst cleaning the temple in great joyousness, He chanted the Hare Krishna maha-mantra. Similarly, all the devotees would also chant while simultaneously performing their separate duties. The entire body of Lord Chaitanya was covered with dust and dirt. In this manner it became transcendentally attractive. Many a time, when cleansing the temple, the Lord shed tears, and in some places He even cleansed with those tears.
After Sri Chaitanya Mahaprabhu collected all the straw, dust and grains of sand in one place, He collected it all in His cloth and threw it outside. Following His example of Sri Chaitanya Mahaprabhu, all the devotees, in great jubilation, began to gather straws and dust with their own cloths and throw them outside the Gundicha temple.
When the temple was thoroughly cleaned, it became very purified, cool and pleasing, just as if the Lord’s own mind appeared there. Indeed, after everything had been washed, the minds of the devotees were as clean as the rooms. By enacting this pastime of cleaning the Gundicha temple, Sri Chaitanya Mahaprabhu instructed us on how we should receive Lord Krishna within our heart. If we desire to see Krishna seated within our hearts, we must first of all purify our hearts fully and prepare to receive His lotus feet.
In his Amrita-pravaha-bhasya, Srila Bhaktivinoda Thakura summarizes the Chaitanya Charitamrita Madhya 12 chapter as follows:
The King of Orissa, Maharaja Prataparudra, tried his best to see Lord Chaitanya Mahaprabhu. Sri Nityananda Prabhu and the other devotees informed the Lord about the King's desire, but Sri Chaitanya Mahaprabhu would not agree to see him. At that time Sri Nityananda Prabhu devised a plan, and He sent a piece of the Lord's outward garment to the King. The next day, when Ramananda Raya again entreated Sri Chaitanya Mahaprabhu to see the King, the Lord, denying the request, asked Ramananda Raya to bring the King's son before Him. The prince visited the Lord dressed like a Vaishnava, and this awakened remembrance of Krishna. Thus Sri Chaitanya Mahaprabhu delivered the son of Maharaja Prataparudra.
After this, Sri Chaitanya Mahaprabhu washed the Gundicha temple before the Ratha-yatra took place. He then took His bath at Indradyumna Sarovar and had prasadam in the garden nearby. While Sri Chaitanya Mahaprabhu washed the temple of Gundicha, a Gaudiya Vaishnava washed the lotus feet of the Lord and drank the water. This incident is very significant, for it awoke within the devotee ecstatic love.
Sri Chaitanya Mahaprabhu took great pleasure when He saw the Jagannatha Deity after the period of the Deity's retirement. At that time Lord Chaitanya was accompanied by all the devotees, and all of them were very pleased. by Yashodanandana Dasa
Srila Prabhupada explains Gundica marjana by Yashodanandana Dasa