Certain places are important in Islamic history, in large part because they were important in the life of Muhammad, and are also important to present-day Muslims.
Most of Islam's sacred places are in the Middle East, specifically the Arabian Peninsula. The area of ancient Mesopotamia (mostly in modern Iraq) and northern Africa are important to in Islam as well, even though they are not as equally sacred as places like Mecca and Medina.
The most sacred place in all of Islam is the Ka'ba in Mecca, Saudi Arabia. The Ka'ba is a shrine, built by Abraham according to Muslim tradition, around a black stone. The Prophet Muhammad specifically designated Mecca as the holy city of Islam and the direction (qibla) in which all Muslims should offer their prayers.
The second most important place in Islam is Medina (or Medinah), the "City of the Prophet," is in the Hejaz region of western Saudi Arabia. It was to Medina city that Muhammad fled when he was initially driven out of Mecca, and the place where he attracted his first followers.
The third most sacred city in Islam is Jerusalem, which was the original qibla (direction of prayer) before it was changed to Mecca. Jerusalem is revered because, in Muslim tradition, Muhammad miraculously traveled to Jerusalem by night and ascended from there into heaven.
Karbala is a city in Iraq, located about 100 km southwest of Baghdad. Shia Muslims consider Karbala to be one of the holiest places in the world, second only to Mecca and Najaf.
Najaf is one of the holiest cities in Shia Islam and is the center of Shia political power in Iraq.
Notable Mosques
Al-Aqsa, in Jerusalem
Al-Azhar in Cairo, Egypt - the mosque university is the foremost school of Sunni Islam
Al-Hakim Mosque - one of the largest Fatimid mosques in Cairo, Egypt
Ar-Rifaye Mosque in Cairo, Egypt
Babri Mosque in Ayodhya, India - now destroyed and a site of recent violence between Muslims and Hindus
Badshahi Mosque in Lahore, Pakistan
Bajrakli Mosque in Belgrade, Serbia - burned in 2004 after ethnic violence
Dome of the Rock (Masjid Al Sakhrah) in Jerusalem - technically a shrine, not a mosque
Faisal Mosque in Islamabad, Pakistan
Ferhadija Mosque in Banja Luka, Bosnia and Herzegovina, destroyed in 1993
Great Mosque of Djenné in Djenné, Mali
Ground Zero Mosque, New York City
Hagia Sophia in Istanbul, Turkey - was a mosque from 1453 until 1934; is now a museum
Hassan II Mosque in Casablanca, Morocco
Id Kah Mosque in Kashgar, People's Republic of China
Imam Ali Mosque in Najaf, Iraq - the holiest Shi'ite mosque
Isabey Mosque in near Izmir, Turkey
Istiqlal Mosque in Jakarta, Indonesia - the largest mosque in Southeast Asia.
Masjid al Haram in Mecca, Saudi Arabia - the "Great Mosque"; holiest in Islam
Masjid al Nabawi in Medina, Saudi Arabia
The Mezquita in Córdoba, Spain - now a Catholic cathedral
Masjid al-Quba, just outside Medina, Saudi Arabia - foundation stone was laid by the Prophet Muhammad
Mosque-Madrassa of Sultan Hassan, in Cairo, Egypt
Mosque of Ibn Tulun, in Cairo, Egypt
Mosque of Mohammed Ali at the Citadel, Cairo, Egypt
Selimiye Mosque in Edirne, Turkey
Suleiman Mosque (Süleymaniye Mosque) in Istanbul, Turkey
Sultan Ahmed Mosque ("the Blue Mosque") in Istanbul, Turkey
Tsar's Mosque in Sarajevo, Bosnia and Herzegovina