Cairo, straddling the Nile, is the biggest city in North Africa and the biggest in the Middle East. It's the capital of Egypt and one of the leading cities in Islam. With about 20 million people in greater Cairo, it's bursting at the seams and pulsing with energy.

Cairo's downtown is modern and can feel European. Streets, squares, and grand buildings are reminders of the country's colonial past — from the 19^th and early 20^th centuries.

The riverfront throbs with energy — stately bridges busy with traffic, fancy riverside restaurants, and towering apartment complexes. The Nile is still the lifeblood of the city, sprawling endlessly on both sides.

The heart of Cairo is Tahrir Square. It's long been ground zero for the people's spirit. If there's a demonstration going on — and there have been massive ones in recent years — it's likely here. In addition to its political energy, the city's long been a religious capital.

Ever since the forces of Islam swept across North Africa from Arabia in the seventh century, spreading the teaching of their prophet Mohammed, Cairo has been a leading city of the Muslim world.

And today, Cairo's known as the city of a thousand minarets.

Stepping into the Al Hussein mosque, like [with] any neighborhood mosque, you'll find a worshipful tranquility. It's believed that resting here invigorates the soul. There's more intensity around the adjacent shrine, believed to contain a sacred relic: the head of Al Hussein ibn Ali, a grandson of the Prophet Mohammed.

In a mosque, men and women worship separately. As praying can be physical, with lots of bending over, it's considered more respectful to allow woman their own space. I find that a respectful tourist is welcome to be a part of the scene.

Along with minarets, you'll see church spires — especially in Cairo's Coptic quarter. While Egypt is predominantly Muslim, today about 10 percent of the country is Christian. The Egyptian, or "Coptic," Church actually predates Islam by six centuries.

Because they worship in an orthodox style, stepping into a Coptic Mass is like going back in time.

The faithful believe that when Mary, Joseph, and baby Jesus escaped Herod by fleeing to Egypt, this very spot is where they took refuge. Later, in AD 43, it's believed the Evangelist Mark came to Egypt and established the Coptic Church. Mark was their first pope and the first in an unbroken line of Coptic popes stretching back nearly 2,000 years.

The Coptic quarter comes with high security. Throughout Egypt, travelers will notice armed guards, security barriers, and a high-profile police presence. These are reminders of a pent-up tension in Egyptian society. They reveal the challenges Egyptian democracy faces today.