Photo by @usman_zubair of a beautiful view of Jamia Masjid located in Rawalpindi, Pakistan.

Bernard O'Kane, a professor of Islamic art and architecture at American University in Cairo, has a message and a nudge for travellers standing outside a mosque, wondering whether they should enter: Go inside.

An object of architectural beauty and cultural fascination awaits.

His new book, "Mosques: The 100 Most Iconic Islamic Houses of Worship," isn't a guidebook per se; the coffee table tome weighs 9kg.

But his selections are inspiring and deserve a time slot in any travel itinerary. To better understand mosque construction and design, as well as visitor etiquette, we reached out to O'Kane at his home in Cairo. The interview has been edited for style and space.

Question: What is a mosque?

Answer: A mosque is created for anyone who makes a space set aside to pray. There's no architectural definition of a mosque, which means there's an enormous variety of possible spaces.

Q: Do mosques share similar characteristics?

A: You can make your own personal mosque by marking off a space to pray, but the mosques people visit communally will have some distinguishing features, such as a mihrab, a niche in the center of the wall facing Mecca. The qibla wall is a commemoration of the place where the prophet Muhammad led the first prayer.

Q: Why did you choose these mosques?

A: I was asked to pick 100, basically what I thought were the most representative and exciting buildings. I also wanted to give some idea of the geographical and chronological range of the buildings.

Q: Did you visit all 100?

A: I visited 80 to 85 percent of them.

Q: What is inside mosques, and do the interiors vary?

A: There aren't really any surviving old mosques that have the exact furnishings from when they were built. The carpets, if they were old, would have been transferred to museums. In Turkey, for instance, in the middle of the 20th century, they found some extraordinarily old carpets in some of the medieval mosques, but they are now in the carpet and rug museums in Istanbul. Most mosques have pulpits called minbars, which are frequently made of carved wood, tile or stone. Some have wooden stands for Quran readers and smaller stands on which Qurans are placed. Of course, the decorative materials can differ substantially. Places with good stone for quarrying used the material for building and decoration. When stone wasn't available, they used brick. Initially they laid it in different ways to create decorative patterns, but later on, from the 14th century, colored tile revetment became very popular. Iran and northwest India favored tiles.

Q: Which mosques would you recommend visiting?

A: I lived in Iran for a few years, and some of my favorite mosques are in Isfahan, which is one of the most beautiful cities in the world. But there are also other cities like Istanbul, Cairo and Delhi that have an amazing concentration of buildings from a wide range of periods. This is an excellent way to get the feel of an Islamic city.

Q: Non-Muslims are not permitted to go to Mecca, correct?

A: That's correct. While Mecca might be an amazing experience, the Saudis have unfortunately not been keen on preserving any of the old buildings and have knocked most of them down to build new structures.

Q: Can you suggest a portable book on this subject?

A: I can recommend one of my own that's smaller and lighter. It's called "Treasures of Islam: Artistic Glories of the Muslim World." It includes art as well as architecture. But a pocketbook for travel? I don't really think there is one that covers the whole Islamic world.

Washington Post