1. Segovia, Castile and León
What to do? Less than 60 miles northwest of Madrid, Segovia is home to two UNESCO World Heritage sites: the Old Town and the Roman aqueduct. Each is worth a visit. The two-tiered aqueduct was built around 50 A.D. and is one of the best-preserved aqueducts in the world.
Fun fact: If the castle pictured above looks familiar, there's good reason: The Alcázar de Segovia, which first served as a military fortress, is rumored to have inspired the design of Cinderella's Castle at Walt Disney World.
2. Santillana del Mar, Cantabria
What to do? Take a stroll through this well-preserved medieval town, located on the northern route of the Camino de Santiago, and be transported back in time. The town's romanesque Collegiate Church, which is flanked by two stone lions, dates back to the 11th century.
Fun fact: The historic Altamira Caves are a five-minute car ride from Santillana. Historians believe the cave paintings of animals and unidentified signs are among "humanity’s earliest accomplished art."
3. Salamanca, Castile and León
What to do? The University of Salamanca, which has been in operation for some 750 years, was considered one of the finest universities in the world during the Middle Ages. Today, visitors can admire the Gothic, Renaissance, and Baroque architectural styles of the campus.
Don't miss: Though not constructed until 1729, Salamanca's Plaza Mayor is "the most sumptuous of the Baroque squares in Spain." If you visit during the school year, be prepared to find the plaza filled with college students.
4. Granada, Andalusia
What to do? A monument to Spain's rich history, the Alhambra was built in the 13th and 14th centuries when Spain was controlled by Arab rulers. The palace complex is home to courtyards and fountains and was the "largest political and aristocratic center" of Muslim Spain.
Don't miss: Situated above the modern part of the city, the Moorish residential area of Albayzín is a relic of days gone by, "its narrow streets and small squares" beckoning visitors to stroll around and discover its past.
5. Albarracín, Aragon
What to do? Located some 110 miles inland from Spain's Mediterranean coast, Albarracín seems almost untouched by modern civilization. The sights visitors take in while wandering around the village's narrow streets are rivaled only by the views of the surrounding mountains and the Guadalaviar River below.
Fun fact: Climb the historic Tower of Doña Blanca for breathtaking views of the town and nearby mountain range. Legend has it that the spirit of Doña Blanca, who died in the tower, "leaves on a full moon in August to take a dip in the Guadalaviar River below."
6. Logroño, La Rioja
What to do? While the walls that once surrounded the city are no more, the two parts that remain, the Revellín Wall and the Carlos I gate, provide the backdrop for "ceremonies which commemorate the French siege of the city." The Cathedral of Santa María la Redonda and the Santa María de Palacio church dominate the skyline with their towering architecture.
Don't miss: About an hour's ride south of the city is Enciso, where visitors can find a paleontology museum profiling the dinosaurs that once roamed the region.
7. Jerez de la Frontera, Andalusia
What to do? Even in the late Middle Ages, Jerez — which means "sherry" in Spanish — was known for its fantastic wine production. Visitors today can explore one of many wine cellars found in the city, such as the historic González Byass winery.
Don't miss: A visit to Jerez isn't complete without stopping by the Carthusian monastery of Santa María de la Defensión in Jerez. Monks living there in the Middle Ages created and bred a particular variety of horses, the Cartujana, which is still celebrated annually.
8. Burgos, Castile and León
What to do? Taking over 300 years to complete, the Burgos Cathedral is a striking example of some of the finest Gothic architecture from the Middle Ages.
Fun fact: For a trip way back in time, visit the Museum of Human Evolution, which documents and explains the nearby archaeological site of Atapuerca. According to UNESCO, "The earliest and most abundant evidence of humankind in Europe" is found in the Atapuerca caves.
9. Pamplona, Navarra
What to do? Known for the Running of the Bulls, which takes place in the city each July, Pamplona has much to offer throughout the year: Visit the city's cathedral, La Navarrería; explore the old medieval city center; or check out the Museum of Navarra, which is housed in a hospital dating to the 1500s.
Don't miss: The Aqueduct of Noain is an absolute must-see. Finished in 1790, the still-intact aqueduct was designed to carry water from the springs of Subiza north to Pamplona.
10. Consuegra, Castile-La Mancha
What to do? Fans of Cervantes' Don Quixote will immediately recognize the towering windmills of Consuegra. In the novel, Don Quixote believes them to be fierce giants and so begins attacking them in vain.
Don't miss: While visiting the windmills, check out the nearby Consuegra Castle, which began being built in the 10th century. Nearly destroyed by Napoleon's forces in 1813, the castle is still being rebuilt.
11. Huesca, Aragon
What to do? Huesca is home to a multitude of beautiful buildings from centuries past: the Gothic cathedral and Diocesan Museum, the church and cloister of San Pedro el Viejo, and the old palace of the Aragonese monarchs.
Don't miss: Just over 20 miles from Huesca is the Loarre Castle. Constructed in the 11th century, the Roman fortress is a foreboding structure, towering over the surrounding area.
12. Avila, Castile and León
What to do? The fortified walls that surround the city are as impressive today as they were when they were built in the 12th century. Still remarkably well preserved, the walls connect to 82 towers and nine gates.
Don't miss: The Baroque-style Convent of Santa Teresa and the Gothic-style Ávila Cathedral are absolute must-sees. The sanctuary of the cathedral is actually built into the walls that surround the city.
13. Girona, Catalonia
What to do? Girona is home to several distinct areas that visitors are drawn to: the medieval quarter, with its mighty Força Vella fortress; the Jewish quarter, with its labyrinthine streets; and area lining the Onyar River, with its brightly colored houses.
Don't miss: The Arab baths, built in the 12th century, are a gorgeous and unique take on the Roman baths that came before them.