Rath Yatra, also popularly known as the Car festival, is celebrated across the globe in the month of Asadh(June/July). This month commemorates the beginning of Monsoons. Although the Rath Yatra is now celebrated globally, the origin of the rath yatra happened in Odisha(the abode of Lord Jagannath), one of the four dhams its origin.and dates back to the Puranas and has a quite interesting story behind its origin.
A majestic procession of the three lords, Lord Balabhadra, Devi Subradra and Lord Jagannath is carried out in three chariots(Taladhwaja,Devadalana,Nandighosh) from Puri Jagannath temple to Gundicha Temple in Puri where the dieties stay for a period of 9 days.
The idols of the trinity are replaced every twelve years with new idols and the process is known as Nabakalebara(the last one happended in 2015). The Bada Danda(the road from the temple entrance to Gundicha temple) comes alive with millions of devotees coming to witness the great festival and get a chance to pull the chariot.
One piece of caution here: If you are not comfortable with crowded areas, you can watch the entire event LIVE on TV. Some restaurants provide balcony view with charges of around 3500-4000 along with free breakfast and lunch. No vehicles are allowed in the area during the entire day, so you may reach a bit early if you want to watch the whole event LIVE.
The pulling of chariots begins quite late(around 3:30 pm). And the chariots are not pulled after sunset and are left on roads. The crowd tends to get thinner post late evening. THis is the time you can venture into the streets and get a clear view of the dieties(although the chariots are guarded).
The deities return to the temple after spending 9 days at the Gundicha temple and the process is known as Bahuda(return) Yatra.
Although Puri attracts visitors the entire year, its the most crowded during Rath Yatra and New Year when thousands of pilgrims pour from across the globe to seek the blessings of the almighty. So if you are planning to visit during these peak days, make sure to book your travel and stay well in advance.
The nearest airport is the Biju Patnaik Airport(Bhubaneswar) and Puri has its own railway station. If you are reaching Bhubaneswar, its best to book a cab and travel by road as you wont want to miss the scenic beauty the place has to offer. There is a place called as Pipili which comes mid-way and is an excellent place to collect souvenirs.
You can chose to stay close to the temple or else book a hotel or resort near the beach(there are some excellent beach view hotels) having their own private beaches.