As a travel destination, the riverfront city is as rich and varied as the country's long history.

From the ruins of a Moorish castle perched atop one of the city's seven hills to a sidewalk café snuggled against an English Visigoth wall, remnants of Lisbon's colorful past are everywhere.

While Western Europe's oldest city has taken steps to overhaul its transportation system, modernize its downtown area, and revamp its waterfront, it's the charm of Lisbon's oldest neighborhoods that most attract visitors.

Number 10.

Vasco da Gama Bridge Completed in 1998, the Vasco da Gama Bridge is a modern feat of engineering.

Named after Portugal's most famous explorer, it was built to alleviate Lisbon's traffic congestion.

Stretching for nearly 11 miles across the Tagus River, the cable-stayed bridge is so long that its builders had to take the Earth's curve into consideration when constructing it.

But as an expense of $1.1 billion, the six-lane bridge is expected to stand for more than a century, ensuring that visitors can experience its breathtaking architecture for generations to come.

Number 9.

Cristo Rei Statue Inspired by Brazil's iconic Christ the Redeemer statue, the Cristo Rei statue rises up from a hill overlooking the Tagus River.

The massive monument was built to express gratitude to God for allowing Portugal to escape the worst horrors of World War II.

It was opened to the public in 1959.

Standing with arms outstretched, the Christ figure is set atop a tall arch with a rectangular observation deck at the base.

An interior elevator takes visitors to a platform beneath the figure's feet for panoramic views of Lisbon.

Number 8.

Praça do Comércio.

One of the star attractions of Lisbon's downtown waterfront, the Praça do Comércio is an expansive plaza flanked by elegant 18th-century buildings.

Portugal's Dom José I made his home here until the earthquake of 1755 reduced it to rubble.

Locals still refer to the square as the Yard of the Royal Palace.

A monument featuring the King on horseback dominates the center of the plaza.

A large triumphal arch, completed in 1873, anchors the northern side.

Hotels, shops and restaurants located nearby make this sunny square a popular destination for visitors exploring Lisbon's scenic waterfront.

Number 7.

Monument to the Discoveries.

The mammoth white stone Monument to the Discoveries stands like a ship with sails unfurled at the shoreline of the Tagus River where many of Portugal's most important voyages of exploration began.

It was built as a memorial to Dom Henrique, who later became known as Prince Henry the

Navigator.

The prince, who ushered in Portugal's Age of Discovery, is featured at the prow of the stone sculpture with other national heroes and explorers lined up behind him.

Number 6.

Rocio Square.

There's no better place in Lisbon to soak up the local atmosphere than at Pedro IV Square,

Lisbon's most famous plaza.

Located in an elegant district in central Lisbon, the Rocio has been the city's main gathering place since the Middle Ages.

During the Inquisition of the 16th century, the square served as a setting for public executions.

Today, it's the place where friends meet up to enjoy a beverage at a cafe or bar before attending the National Theatre located on the north side of the square.

Number 5.

Lisbon Oceanarium.

One of the best modern tourist attractions in Lisbon, the Oceanarium was built as part of the improvements the city made when it hosted the 1998 World Exposition.

Located in northeast Lisbon, the Oceanarium is the largest indoor aquarium in Europe.

It's organized into four unique habitats, with each representing a different ocean.

In addition to all manner of sea life ranging from sharks to penguins, flora from each ecosystem are represented as well.

Number 4.

Geronimo's Monastery.

With its Gothic and Moorish influences, the striking architecture of Geronimo's Monastery makes it a must-see attraction for anyone visiting Lisbon.

Located in the city's riverside Belém district, the monastery is a piece of carved stone portals, latticework ceilings, and windows with tracery set upon delicate mullions.

In the nave of the church is the tomb of Vasco de Gama, whose voyages to India made Lisbon a wealthy maritime city.

Number 3.

Tram 28.

Most of the decades-old trolley cars that were once a primary mode of transportation in Lisbon are long gone, but visitors can still enjoy a ride in an antique streetcar on Tram Line 28.

The historic Eléctrico takes passengers through the city's oldest sectors, past some of

Lisbon's most popular sights.

Tourists often take Tram 28 to the hilltop São Jorge Castle to take in the panoramic views, but the line is used by locals for their daily commutes, too.

Number 2.

São Jorge Castle.

One of Lisbon's oldest treasures, São Jorge Castle is situated at the top of a hill in the Alfama district.

The castle evokes the period when Lisbon was under Moorish rule, but the site was fortified centuries earlier when the Romans were in power as well.

After driving out the Moors in 1147, the Portuguese used the castle as a royal residence until the early 16th century.

Climbing the ramparts is a must-do activity in Lisbon, and it's easy to understand why.

The views from the parapets and battlements are simply breathtaking.

Number 1.

Belém Tower.

Belém Tower, also known as the Tower of Saint Vincent, sits on what was once an island in the Tagus River.

Founded back to 1515, the imposing tower was built both to defend Lisbon from invaders and to welcome the city's friends.

Built in the Age of Discovery, the four-story limestone tower has a bastion connected to it.

The bastion had space for 17 cannons that could fire long-range shots.

A statue of Our Lady of Safe Homecoming, designed to protect sailors on their voyages, faces the river.