Sacred space in the Islamic world is most obviously found in mosques and in Mecca, the holiest city in Islam. In addition to the major pilgrimage called Hajj, which takes place in Mecca at a particular time on the Islamic calendar, lesser pilgrimages abound in the Sunni world, and have for centuries. These minor pilgrimages, called ziyarat (literally, visitations), are usually to the tomb or shrine of a historical figure who was important in the history of Islam, and whose importance is usually construed in terms of saintliness.
The word ziyara (the singular form of ziyarat), which means "visitation," corresponds to "minor pilgrimage" (as opposed to the Hajj to Mecca, a major pilgrimage.) Pilgrims to the shrine of a local holy man or woman (a great shaykh or mystic/Sufi) literally visit the person who is entombed. They consider the place to be particularly blessed. Often pilgrims will approach a tomb or shrine reverently, kissing the doorway or kneeling at the tomb itself to make supplication. There is even a branch of literature called adab al-ziyarat, the "etiquette of ziyara," that discusses proper behavior for visiting a shrine or tomb.
Architecturally, tombs are usually topped by a dome or cupola. These shrines are richly adorned and often lavishly decorated. Pilgrims occasionally leave notes of supplication or pieces of cloth at a shrine, as a votive symbol of their visitation. Often, money is left for the upkeep of the shrine.
Shrines may also exist within larger buildings, such as the shrine to John the Baptist. The shrine looks like a small domed building, but it actually sits inside the main hall of the Great Mosque of Damascus. In other cases, such as the Eyyup shrine outside Istanbul, a massive mosque and school complex developed around the shrine, in this case the tomb of the Companion Abu Ayyub al-Ansari, who died during an unsuccessful siege against Constantinople in the 7th century. Holy spaces such as this one beget other holy spaces: a miraculous healing fountain is said to have sprung up near Ayyub's tomb, and was visited by Muslims and Christians in the Middle Ages.
It should be said that in the history of Sunni Islam, the issue of sacred space, in terms of ziyara, has been a contentious one. Pilgrimages of this variety have been an important aspect of life in Muslim society, from the Middle Ages to the modern era. But just as the early Christian cult of saints, relics, and icons had its detractors, so too has the Sunni world demonstrated a range of views on the legitimacy of these minor pilgrimages. Some even went so far as to consider them blasphemous, on a par with idolatry, especially the aspect of pilgrims supplicating or kissing a shrine or tomb.
Important medieval theologians like Ibn Taymiyya (1263-1328) eschewed these types of pilgrimages, as well as the festivals (usually celebrating a holy man or woman's birthday) that went along with them. In his view, the only legitimate pilgrimage was to Mecca. Others were diametrically opposed to this view, and espoused their belief that the physical location of a saint's tomb or biblical shrine (such as the cave outside Damascus where Cain supposedly slew Abel, called the Grotto of the Blood) was actually hallowed ground, that it contained more blessing than other land.
These latter authors and scholars, such as Muhammad ibn Suleyman al-Raba‘i (10th century) argued that prayers and supplications made at such loca sancta, especially in Jerusalem, were more efficacious than those made in ordinary spaces. Throughout the Middle Ages and early modern period, a literature known as fada'il or "religious merits" extended to include cities in the Islamic world that housed these types of monuments. From the 10th century on, even small towns and villages in Syria, boasting the tombs of prominent Prophetic Companions, capitalized on the idea that even large landscapes could be sacred.