Marksburg Castle high above the town of Braubach on the Rhine River is believed to date back to the early 12th century - and has remained intact to this very day. It's the only castle built on a hill along the Middle Rhine Valley that was never destroyed. Since 2002, the Upper Middle Rhine Valley is listed as a UNESCO World Heritage Site. On average, you'll see a castle every 2.5 kilometers.

It's arguably Germany's most important castle. Built around 1067 above the central German town of Eisenach, Wartburg provided sanctuary to a fleeing Martin Luther in 1521-22. Here, he translated the New Testament into German. In 1206 it featured the legendary minstrel singing contest portrayed in Richard Wagner's opera "Tannhäuser." Wartburg has been a UNESCO World Heritage Site since 1999.

In medieval times, Nuremberg Castle was a prominent imperial palace. Emperors and Kings of the Holy Roman Empire resided here over the centuries. Demolished in World War II, the castle was rebuilt true to its historic architecture.

Eltz Castle featured prominently on the back of Germany's 500 Deutsche Mark note, making it one of the country's best known castles. Built in the early 12th century in a spectacular location at the top of a 70-meter (230-foot) rock spur in the hills above the Moselle River, Eltz Castle today is a tourist magnet.

Perched above the town of Burghausen in Upper Bavaria, it is the longest castle complex in the world, at least according to the Guinness Book of Records: it measures 1051 meters. The castle was built before 1025 and served as a residence to the Bavarian Wittelsbach dynasty.

First mentioned in 1323, Rheinstein Castle is also situated in the Upper Middle Rhine Valley. In 1823, builder and architect Karl Friedrich urged Prince Friedrich of Prussia to buy the castle that had fallen into disrepair in the late 16th century. In the Romantic period, Rheinstein Castle was the first Rhine River castle to be reconstructed.

It's the largest castle built on a hill along the Moselle River and is a prominent landmark for the town of Cochem. Cochem Castle was presumably built around the year 1100 and destroyed in the 17th century. Berlin entrepreneur Louis Ravené bought it for 300 gold marks and rebuilt the castle in neo-Gothic style around 1877, according to the romantic notions of a knights' castle.

In 1914, teacher Richard Schirrmann opened the world's first youth hostel here. Altena Castle in North Rhine-Westphalia is over 800 years old. After falling into disrepair over the centuries, its reconstruction was completed in 1918.

One of the best-preserved German castles with a moat can also be found in North Rhine-Westphalia. Called the Satzvey Castle, it dates back to the 12th century. Daunting moats were dug to keep hostile enemies at bay. In flat regions, they were an alternative to perching the castle on a rocky cliff or hill.

The spectacular appearance of Hohenzollern Castle in this photo is due to the effects of thermal inversion. The structure lies atop the 855-meter mountain of the same name in Baden-Württemberg. In 1850, Prussian rulers had the one-time residence of their ancestors rebuilt in its current, idealized form. Rulers of the German Empire were drawn from the Hohenzollern dynasty from 1871 to 1918.

Not much remains of this once grand structure. The ruins are located on a point of land that juts into the sea on Cornwall's west coast. But if you visit at dawn or sunset, and hear the wind whistling across the land, you can almost picture King Arthur and his Knights of the Round Table. This is where, according to legend, Arthur was conceived.

The fortress has served as a royal palace, an armory, a treasury and even a zoo, housing elephants, monkeys and rhinoceroses. Now, only ravens live in the tower, which is almost 1,000 years old. They are known as the guardians and legend has it that the kingdom and the tower will fall if they ever leave. To make sure that this does not happen, they all have one wing trimmed.

The castle is perhaps best-known as the refuge of Pope Clement VII, who fled there when Rome was sacked in 1527 by troops of the Holy Roman Empire. From the 17th century until 1870, the Papal State used the castle as a prison. The structure stands on the right bank of the Tiber River. It originally served as a mausoleum for the Roman Emperor Hadrian, who died in 138.

The church was built in the 14th century, and has been a UNESCO World Heritage Site since since 1993. For centuries, local residents fled to churches when invaders threatened their homes - because the churches were often the only structures in the region that were made of stone.

This ancestral castle of the Fleckenstein family is located in the Alsace region of northeastern France, right on the border with Germany. It was built in the Middle Ages atop a narrow sandstone ridge. The castle offers spectacular views of the surrounding countryside - including the Vosges Mountains, the Palatine Forest, and several other castles.

Johann Wolfgang von Goethe visited the castle no less than 10 times. On August 28, 1823, he celebrated his 74th birthday there - along with the family of the young woman he intended to marry, 19-year-old Ulrike von Levetzow. Ulrike declined Goethe's proposal. As he returned to Weimar by coach, Goethe wrote the "Marienbad Elegy," a poem that is considered one of his finest and most personal works.

The oldest part of the castle dates back to the ninth century. The structure was built on a 70-meter-high rock spur in the hills above the Mosel River in the Rhineland Palatinate. The castle has been owned by various branches of the Eltz family for more than 30 generations. Over the course of centuries, the castle has been renovated and expanded - which explains its distinctive architecture.

This castle complex is built on a ridge in southern Bavaria - and at more than 1,000 meters, it's the longest structure of its kind in the world. In the late 12th century, the castle came under the control of the Wittelsbach dynasty. At one point, it was said to be the most secure fortress in Bavaria - and also served as a storehouse for Wittelsbach treasures.

The castle is located on a hill near the Vistula River in Kraków, which was the capital of the Kingdom of Poland for more than 500 years. The first stone structures were built in the 10th century - and various expansion and reconstruction projects continued into the 20th century. Wawel Castle offers visitors a unique perspective on 1,000 years of Polish history.

The first mention of the castle appears in a document written in 1080 by Bruno, bishop of Merseburg. In 1206, the legendary "minstrel contest" was said to have taken place at Wartburg. This competition is featured in Richard Wagner's opera Tannhäuser. In 1521, Martin Luther sought refuge at Wartburg and translated the New Testament from Greek into German.

This castle sits on a 855-meter-high promontory in the Swabian Alps. It is the ancestral seat of the imperial House of Hohenzollern, which ruled Prussia from 1525 to 1918 and Germany from 1871 to 1918. It's one of the most beautiful castles in Europe. The main attractions are a collection of royal artifacts, including the crown of Wilhelm II, and exhibits on the life of Frederick the Great.