MECCA

Location: Mecca, Saudi Arabia Most frequented by: Muslims trip to Mecca isn't likely to be confused with anything but a pilgrimage. Located in a drab, sandy valley about 50 miles from the Red Sea (where summer temperatures can easily reach 115 F), it's hardly a vacation destination. Regardless, it's a must-see for followers of Islam … and we do mean "must." Mecca is the birthplace of the Islamic prophet Mohammed and therefore the holiest city to Muslims.

In fact, one of the religion's "Five Pillars" requires followers to attempt a hajj, or pilgrimage to Mecca, at least once during their lives if at all physically and financially possible. Not ones to take pillars lightly, more than 2.5 million devout Muslim pilgrims flock to the city each year. The hajj takes place during Dhu'l-Hijja, the last month of the Muslim calendar year (which is based on lunar cycles, meaning the hajj dates change annually).

While there, pilgrims follow a pattern of devotional duties. One such ritual involves circling the Ka'ba, a cube-shaped building said to be the first place Mohammad preached and the holiest shrine in Islam. In addition, pilgrimages include the ritual kissing of the Black Stone. Although not a formal object of Islamic veneration, the Black Stone is believed to be a meteorite and is revered by pilgrims as a traditional symbol of Mecca.

According to Muslim legend, it was originally a white stone given to Adam after he was expelled from Paradise, and since then, it's turned black from absorbing the sins of all those who have touched or kissed it. Sadly, pilgrimages to Mecca are sometimes marred by tragedy. In 1990, a human stampede in an underground pathway resulted in nearly 1,500 deaths. And in 2004, another stampede killed 251 worshippers.. But Mecca's potential dangers are less of a threat to non-Muslims. Members of all other religions are banned from the city to prevent its sanctity from being "polluted."