Every year, upwards of 135,000 music fans camp among stages in the fields of Glastonbury, a small town in Somerset, England. The influx of people who come from all around the world for the weekend festival swells the population roughly 1,560 percent.

During the month of March, hundreds of thousands of students in U.S. colleges and abroad vacate their campuses to blow off some steam in tropical locations. Top destinations such as Cancún, Puerto Vallarta, the Bahamas, Miami Beach and Panama City Beach, FL, see a wave a students descend, with Panama City Beach alone estimating 400,000 visitors during the Spring Break period.

Every four years, thousands of people around the world migrate to a different host city for a month to catch the FIFA World Cup. In 2010, an estimated 370,000 visitors flocked to South Africa to catch their teams in action.

Under the reign of Saddam Hussein, openly celebrating Arba'een was illegal. Since his fall from power, hundreds of thousands of Shia Muslims head to Karbala, a city south of Baghdad, to mark the religious rite. The event marks the end of a 40-day period of mourning after the death of Imam Hussein, a grandson of the prophet Muhammad, who was killed in the seventh century. The continued tensions between Shia and Sunni Muslims in Iraq have resulted in terrorist cells planning bombings during the religious pilgrimage in recent years.

In 2009, this 10-day annual festival saw 2.5 million women descend on the area near the Attukal temple in Kerala to give offerings to the Hindu goddess Bhagavathy — an incarnation of the goddesses Kali and Saraswati. What used to be a traditional smaller pilgrimage and festival, in recent years, has become the Guinness World Record holder for the largest annual gathering of women.

The fifth and final pillar of Islam is the Hajj, a pilgrimage which every able-bodied Muslim must complete once in their lifetime if they can afford it. During the month of Dhul Hijjah, the twelfth month of the Islamic lunar calendar, upwards of 2 million Muslim pilgrims travel to Mecca in order to take part in the rite.

Thanksgiving has always been one of the largest travel holidays for Americans. In 2010, it was estimated that 42.2 million people would be driving over 50 miles for their Thanksgiving celebrations, in addition to 24 million Americans flying during the holiday period.

The annual two-month festival at the Sabarimala temple in Kerala attracts between 45 and 50 million pilgrims each year. During this time, pilgrims make their way up a hillside to enter the Sabarimala temple where the Hindu god Ayyappan is believed to have meditated. The mass of pilgrims is primarily composed of men, as women aged 10 to 50 (those of typical reproductive age) are not allowed inside the temple, due to the fact that Ayyappan was celibate in Hindu mythology.

The Hindu festival of the Kumbh Mela commemorates a celestial battle between gods and demons. Because the battle lasted for 12 divine days, a full Kumbh Mela is celebrated every 12 years. The time in between this is split up by an Ardh Kumbh Mela which occurs every six years. The most recent Maha Kumbh Mela which occurred in 2001 drew an astounding 70 million pilgrims to the Sangam (where the Ganges and Yamuna rivers meet).

The Chunyun period, or Spring Festival Rush, refers to the time around Chinese New Year when millions of migrant workers and students leave the cities of China to return home for festivities. During this period, upwards of 120 million people migrate home on extremely crowded trains and planes which they sometimes must wait days in order to board.