To reach Turkey's most important Roman Catholic church, a visitor must scour a traffic-choked street to find the metal doors, walk down a flight of stairs, cross a courtyard and finally step into the consecrated basilica.
Inside the Holy Spirit Cathedral here, the lights remain low until a minute before evening Mass, and then reveal frescoed ceilings with gold-trimmed arches, 22 crystal chandeliers and blond-marble columns. On this night, 14 worshipers dot the pews.
In the Turkish capital, Ankara, the only Catholic church is even more discreet: It is marked simply by a French flag.
When Pope Benedict XVI travels to Turkey next week, he will be making his first trip to a predominantly Muslim country at a moment of diplomatic fragility.
He also will be traversing some of the most ancient and revered milestones of Christianity, in a land where Christianity is disappearing and where non-Muslim minorities complain of systemic discrimination, harassment and violence against them.
It is a complex agenda. The pope's main purpose is to meet with the Istanbul-based spiritual leader of the world's 250 million Eastern Orthodox Christians in a show of ecumenical solidarity. But he must also use the visit to attempt to repair the damage from comments he has made that cast Islam in a negative light.
Among Turkey's nearly 70 million Muslims, reaction to Benedict's visit ranges from disinterest to intense anger. A man opened fire early this month on the Italian Consulate in Istanbul, telling police later that he wanted to "strangle" the pope. A nationalist gang called the Gray Wolves is staging regular demonstrations protesting the pontiff's arrival.
Among the estimated 100,000 Christians who live in Turkey, there is hope that Benedict's presence will cast light on their difficulties.
The Roman Catholic Church is not legally recognized in Turkey. It functions largely attached to foreign embassies; its priests do not wear their collars in public.
Most Christians in Turkey are of the Armenian, Greek and other Orthodox denominations, and although most of these are recognized in the Turkish Constitution as minority communities, they face severe restrictions on property ownership and cannot build places of worship or run seminaries to train their clerics.
Such hardships make it almost impossible for Christians to sustain and expand their communities, advocates say. The Greek Orthodox, for example, have dwindled to no more than 3,000, just 2% of the community's size in the 1960s.
Fueled by a vitriolic, and growing, potion of nationalism and Islamic radicalism, spasms of violence have led to the killing of one priest this year, the beatings of two others and the burning of a Christian prayer center. Christian tombstones are often vandalized and property frequently confiscated by authorities.
Turkey has come under repeated criticism from Western human rights organizations and the Vatican for its failure to promote religious freedom. Turkey is an Islamic but secular country; in reality, this means that all religious activity, including mosques and imams, is controlled by the government.
"Obviously, more needs to be done to promote religious freedom for all denominations," Ali Bardakoglu, president of Turkey's powerful Religious Affairs Directorate, said in an interview. But he defended the government's treatment of minorities, contending that Christians and other non-Muslims do not face serious problems.
Bardakoglu was one of the most emphatic critics of Benedict after the pope delivered a speech in Regensburg, Germany, in September that denounced Islamic violence and quoted a medieval Byzantine emperor who disdained Islam and its prophet, Muhammad. Adding insult to injury, as far as many Turks were concerned, the emperor was defending Constantinople, cradle of Orthodox Christianity, against the Muslim conquest that gave the city its name today: Istanbul.
Bardakoglu said the pope was welcome in Turkey despite the speech, which touched off outrage throughout the Muslim world. And although he said he accepted Benedict's subsequent explanations, Bardakoglu did not appear completely appeased.
"It is unfortunate that there are circles within Western society that attempt to blacken the name of our religion and are infected with Islamophobia," he said. "The role of the Vatican and the pope should be to help fight stereotypes. Rather than open debate, they should be seeking to heal wounds."
In a remarkable gesture, the pope will meet with Bardakoglu, the country's top religious figure, at his ministry, a modern, imposing building on Ankara's outskirts, on the first day of his Turkey visit. Bardakoglu's directorate commands a huge budget and oversees all of Turkey's imams.
Originally, the Vatican expected Bardakoglu to call on the pope at the Vatican Embassy, as protocol would have dictated. But the Turks refused. After a series of negotiations, the pope agreed to go to Bardakoglu. "It is a gesture of goodwill," a senior Vatican official said.
The pope's controversial presence in Turkey represents a balancing act for the government of Prime Minister Recep Tayyip Erdogan, which regards itself a vital bridge between the West and East, a way for Westerners to deal with a modern and democratic Islam. But it also cannot appear too cozy with a pontiff who, in the view of many, is not fond of Muslims or Turks.
Erdogan is not scheduled to receive Benedict, citing a previous commitment to attend a NATO summit in Latvia on Tuesday and Wednesday. And there is no plan for the prime minister to see him off when the pope departs Dec. 1.
Both the Vatican and Turkish officials said this was not a snub, but Erdogan told visiting reporters in Istanbul last month, "You can't expect me to arrange my timetable according to the pope."
The frictions are rooted in history. The Ottoman Empire, which ruled the region for more than six centuries, was relatively tolerant of Jews, Christians and other non-Muslims. But before and during World War I, Western powers collaborated with Christian and other minorities to bring down the Ottomans. In the carnage that followed, as many as 1.5 million Armenians were slaughtered, a similar number of ethnic Greeks expelled and 1 million Turks deported from Greece.
The 1923 Lausanne Treaty founded the Republic of Turkey and recognized minorities. But deep mistrust persists, and even today among ardent nationalists, Christians are seen as a potential fifth column.
"It's a kind of preemptive intolerance: Don't let it flourish because it might take over," said Mustafa Akyol, a writer and expert on interfaith relations. "Everyone is afraid of something."
Akyol, a Muslim, said he once wrote a column advocating that the museum of St. Sophia, or Aya Sofya, in Istanbul be returned to its original use, that of a church. The response was harsh: He was threatened and castigated as a "secret Greek." The pope is scheduled to visit St. Sophia, built in the 6th century as a Byzantine church and converted to a mosque in the 15th century by the Ottomans.
The mere rumor that the pope might say a prayer at the site has led to a bit of hysteria. Islamic newspaper Milli Gazete, in a front-page commentary last week, lashed out at the government for permitting the "Crusaders" to plan to bless the former church in a brazen attempt to "revive Byzantium."
For their part, Turkish officials have sought to minimize the pontiff's main mission on this trip: to worship alongside Ecumenical Patriarch Bartholomew I, head of the world's Orthodox Christians. The coming together of the two religious leaders is meant as a bridging of the 1,000-year-old rift between the two ancient branches of Christianity.
Such frictions notwithstanding, Turkey, compared with many Muslim countries, is relatively hospitable to non-Muslims. But its failure to make more progress on freedom-of-religion issues has been an important stumbling block in its years-long campaign to join the European Union.
It is EU pressure that has nudged Ankara along in easing some of the restrictions on minorities; for example, a Protestant group in Istanbul has for the first time been allowed to open a church.
"The EU reforms give people a sense of hope that there is light at the end of the tunnel," said Greek Orthodox Father Alexander Karloutsos. "It's been very dark here."