"He who builds a mosque in the way of Allah, God will build a house for him in paradise." So said Abu Bakr, the first Islamic caliph, and his words have been followed ever since. Throughout the history of Islam mosques have provided the faith with its religious, cultural and communal focus.
They act not only as places of worship but also as schools, community centres, charitable foundations and even (in days past) hospitals and law courts. They are places in which worldly divisions of class, wealth, status and ethnicity vanish, with all becoming equal in the sight of god.
Most mosques around the world are off-limits to non-believers, reinforcing stereotypes and encouraging skeptics to label them as hives of Islamist extremism. Fortunately many of Islam's largest, loveliest and most historic shrines are freely open to all, not only allowing visitors to experience some of the planet's most spectacular buildings, but also to glimpse something of the religious and cultural life of these remarkable monuments to the world's most misunderstood faith.
Morocco's largest city, Casablanca sees relatively few foreign visitors despite its absorbing array of sights ranging from medieval souks to Art Nouveau mansions, strung out along an attractively windswept expanse of Atlantic coastline.
Few who visit, however, pass up the chance to explore the city's landmark Hassan II Mosque. Completed in 1993, the mosque stands on an oceanfront promontory, its enormous minaret (the world's tallest, at 210m) soaring above the coast like an enormous Islamic lighthouse, while the cavernous interior glows with the magical colours of blue marble mosaics, lustrous tilework and enormous pendant chandeliers.
Old Cairo is a virtual museum of mosques, with dozens of historic shrines dotted around the twisting, time-warped alleyways of the medieval centre. Amongst the finest is the stately Aqsunqur Mosque, completed in 1347. Rising above Bab al-Wazir Street, the building's fortress-like walls are capped with minarets and intricately carved domes, while inside stands the mosque's magnificent Mecca-facing eastern wall, entirely covered in a luminous array of azure tiles.
Soaring high above the heart of Istanbul at the meeting point of Europe and Asia, the Sultan Ahmed Mosque (completed in 1616, also known as the Blue Mosque) is generally reckoned the crowning example of Ottoman architecture, with a quartet of needle-thin minarets pointing dramatically skywards and a sumptuously red-carpeted interior smothered in delicate tilework blossoming with thousands of stylized blue tulips.
If it were almost anywhere else in the world, Isfahan's great Naghsh-e Jahan Square would be teeming with tourists. Present-day political and practical realities mean that those who make it to Iran can enjoy an authentically foreigner-free taste of the world's most perfectly preserved Islamic architectural set-piece.
The square is home to not one but two of the planet's most stunning mosques, the Shah and the Jameh (Masjed-e Jameh) mosques. The Jameh Mosque is the larger and the older of the two, dating back to pre-Islamic Zoroastrian times and has been rebuilt continuously over the centuries to produce the stunning complex you see today, with three stupendously huge, blue-tiled porticoes rising around a vast courtyard, and mirror-perfect reflections in the ablutions pool between.
One of the world's oldest and most revered Islamic shrines, Damascus's Umayyad Mosque dates back to 715, less than a century after the Muslim faith first burst spectacularly into the world. The monumental building itself reflects the changing times in which it was built, adorned with Classical Roman-style Corinthian columns and Byzantine-style mosaics alongside the first of the great congregational courtyards which subsequently became the norm throughout the Islamic world.
Looming above the approach roads to Abu Dhabi like a vast wedding cake – with minarets – the Sheikh Zayed Mosque (completed 2007) offers a gigantic monument to the Muslim faith in a region now better known for its seven-star hotels, record-breaking skyscrapers and palm-shaped artificial islands.
Perhaps not surprisingly, Abu Dhabi's shiny new mega-mosque boasts its own string of record-breaking attractions: the world's largest carpet lives here, along with the planet's largest marble mosaic. Although it's the serene beauty of the overall conception, with vast expanses of lustrous marble and myriad dazzling domes shining snowy white in the fierce Gulf sunlight, which really lingers in the memory.
A majestic monument to India's great Mughal rulers, rising in stately splendour above the tangled labyrinth of hectic streets at the very heart of Old Delhi. Commissioned by Shah Jahan, creator of the Taj Mahal, the Jama Masjid remains an unequalled symbol of Islamic architecture in a largely Hindu country, with soaring minarets, delicate marble domes and a vast prayer hall – as well as peerless views across the teeming melée of the old city from its vast courtyard, raised high above the streets below.
Some sixty miles north of Baghdad, the Great Mosque of Samarra is one of the oldest and most unusual in the Islamic world (although currently off limits to casual visitors, for obvious reasons). The world's biggest mosque when it was completed in 851, the building was largely destroyed during the Mongol invasion of 1278 save for its outer walls and unique minaret, the so-called Malwiya Tower, a remarkable conical structure 52m high wrapped in a spiral staircase, like a gigantic upended telescope rising surreally from the desert sands.
The most enduring reminder of Islam's centuries of rule in Western Europe, Cordoba's Mezquita was built on the site of an early Christian basilica following the Muslim conquest of Spain and finally completed in 987 – before being returned to use as a church in 1236.
A miniature Renaissance cathedral was unceremoniously shoehorned into the heart of the building during the sixteenth century, although this does little to mask the building's Islamic, quintessentially Moorish character, with its endless rows of jasper, onyx and marble pillars – "like palm trees in the oases of Syria" as one visitor described it – with red-and-white horseshoe arches and a dazzling mihrab.
Opened in 2016, the Diyanet Center Mosque is one of the largest and certainly the most beautiful of the many mosques serving the USA's 3.3 million Muslims. Designed in classic Ottoman style, the mosque was part-funded by the Turkish government and was built with Turkish marble.
Opposition to the "mosquestrosity" (as its critics dubbed it) was considerable, but supporters hope that the building will provide a valuable symbol of religious tolerance and cultural diversity to the country at large – not least to the current incumbent of the White House, just 21km down the road.