PURI, INDIA, June 26, 2023 (Indian Express): Millions of visitors from across the globe throng the beach town of Puri in Odisha to take part in the annual Rath Yatra (car festival) of Lord Jagannath, which this year began on June 20. According to Hindu mythology, the Lord along with his siblings — elder brother Lord Balabhadra and sister Devi Subhadra — embarks on a nine-day annual sojourn to his birthplace. The statues are taken to the Gundicha Temple, where they stay till the Bahuda Yatra (returning car festival), scheduled on June 28 this year.

The Rath Yatra takes place on the second day of the Odia month of Ashadha Shukla Tithi (bright fortnight) every year to commemorate the journey of Lord Jagannath and his two siblings from their abode —the 12th century Jagannath Temple, to the Gundicha Temple, believed to be their aunt’s home. Goddess Ardhasini, also known as Mausima, is believed to be the Deities’ aunt. The Deities board three huge decorated chariots following the Pahandi ritual (ceremonial procession), before marching for around 1.86 miles to the Gundicha Temple. Millions of devotees pull the chariots on the Bada Danda (Grand Road) of Puri town.

For details on the various rituals of the nine-day festival see source.
https://indianexpress.com/article/explained/explained-culture/rath-yatra-in-puri-significance-of-the-deities-journey-to-their-aunts-place-8685726/