In Islam, Muslims have three holy cities: Makkah, Medina, and Jerusalem.
Makkah is importnat because they beleive that Prophets Abraham and Ishmael (the father of the Arabs) built the cube-shaped Ka'bah, as a place of worship for the One God, the House of God. Muhammed was born in Makkah, Arabia and Makkah itself is the birhplace of Islam.
The story of building the Ka'bah is told in the Quran: "And when We assigned to Abraham the place of the House (Kaaba), saying: Do not associate with Me aught, and purify My House for those who make the circuit and stand to pray and bow and prostrate themselves" AND "And when Abraham and Ishmael raised the foundations of the House (Kaaba): Our Lord! accept from us; surely Thou art the Hearing, the Knowing"
Medina (Arabic for the city) is the second most sacred city in the Islamic World after Makkah.Prophet Muhammad immigrated to Medina in 622 CE to escape the persecution of the pagan Arabs. Since then, Medina became the capital of the Muslim World where the Prophet's Companions managed the affairs of the growing Muslim community.
Prophet Muhammad died in 632 CE, and he was buried under the green dome of the Prophetic Mosque built right after the Muslim emigration of Medina. Therefore, this city holds a special place in the hearts of Muslims.
In Islam, Jerusalem is the third holiest city and the site of Prophet Muhammad's ascension into heaven. Jerusalem houses the Al-Haram Al-Sharif (The Abode of Holines) which is the location of the black-domed Al-Aqsa Mosque and the golden-domed monument The Dome of the Rock.
Muhammed's ascension to the heavens from Jerusalem is mentioned in the Quran: "Glory to He (God) Who did take His servant for a Journey by night from the Sacred Mosque (in Makkah) to the farthest Mosque (Al-Aqsa Mosque), whose precincts We did bless". Muslims believe Muhammed travelled to Jerusalem from Makkah (before immigrating to Medina) on a celestial creature called "Al-Buraq" (Arabic for Lightning).
Jerusalem is also special for the Muslims because it is the land of the Prophets, the birthplace of Jesus (Mulsims believe Jesus was one of the Great Prophets sent down by God), and the site of Cave of the Patriarchs in Hebron and they have many other old mosques there as well. In Jerusalem there is a mosque built by Saladin's son called "Mosque of Umar" (in honor of Islam's second rightly-guided Caliph Umar ibn Al-Khattab).