October represents what is often the last gasp of sunny weather in Spain before rains become commonplace in November. You can expect daily averages in Spain to be around 70°F/21°C with nighttime temps dipping down into the mid or low 50s (Fahrenheit).
Of course, Spain is such a large country that you can expect micro-climates throughout the nation—in other words, it's going to be a lot warmer in the Canary Islands than it will be in the northern Atlantic coast and Basque Country. Using that example, the Canary Islands will still be averaging temps just south of 80°F/26°, which makes for a great beach holiday.
Similarly, the Mediterranean coast and cities like Barcelona and the region of Andalusia will see averages in the mid-70s (Fahrenheit), which will be great for sunbathing but perhaps a bit chilly for swimming.
Obviously the further north you go the lower the temperatures will be. Madrid's average daytime temps are in the high 60s (Fahrenheit) but can dip into the 40s at night. You can expect similar averages in and around San Sebastian.
Crowds & Costs
October is the last month to take advantage of not just consistently good weather in Spain, but lower shoulder-season prices too. You'll find steep discounts on airfare during this month and discounts of 20% or more on many hotels. Remember that Spain's economy is steeped in tourism, and with many vacationers having left the country by October, hotels and airlines will be competing more aggressively for business, which translates to big savings for savvy travelers.
Where to Go
With milder temperatures but still sunny weather, this is the month to experience Spain's incredible and historic cities. You can take walking tours of Madrid, Barcelona, Granada, Salamanca, and Córdoba, and you don't have to worry about the oppressive summer heat. In Madrid alone, there are a number of great sights to visit on foot, from the Plaza Mayor and El Retiro Park to the Museo del Prado and the Puerto del Sol, that other iconic plaza with its famous clock tower.
October is also a great month to head to northeastern Spain's Aragon region. The capital of Aragon is Zaragoza, a stunning city overlooking the Ebro River. It's filled with uniquely beautiful Mudéjar architecture, grand 18th-century basilicas, Medieval Islamic palaces, and the historic Plaza of Our Lady of the Pillar, which is home to the iconic riverside cathedral of the same name.
Zaragoza is definitely worth a visit, particularly if you're traveling in Spain in early October, as Zaragoza hosts the biggest festival in the nation in October, the Fiestas del Pilar (more on this below).
What to Do
This might be the last month to plan an extensive road-trip on Spain's sunny Mediterranean coast (at least, if you want good weather during your drive). You could mix and match any coastal itinerary you so choose, be it a brisk day trip from Barcelona down to Valencia, or a tour of of the Andalusia region from Málaga down along the famed Costa del Sol, which passes through the historic coastal retreat of Marbella.
If the coast isn't beckoning, you might still want to visit Andalusia, as the mild temps won't be as oppressively hot as in summer. This will make a sightseeing and cultural excursion to its capital of Seville a pleasant prospect. Visit the famous Plaza de Espana, a marvel of renaissance-revival architecture.
You could also relax in the largest green space in the city, Maria Luisa Park, take a romantic stroll along the Guadalquivir River, and of course, enjoy a flamenco show at a local tablao (performance space). Flamenco was born in Andalusia, and there's no better place to see a live performance than its capital.
Events in October
Fiestas del Pilar. This annual festival celebrates the patron saint of Zaragoza, the Virgin del Pilar, typically beginning on the weekend of the 12th of October and continuing through the following Sunday. For a week straight Zaragoza is abuzz with live music concerts, food stalls, processions, church masses, carnival rides, and more. The high point occurs on Oct. 12th with the Offering of the Flowers, where thousands of revelers dress in costumes leave flowers at an altar of the Virgin on the Plaza del Pilar.
Fiesta Nacional de España. Held on the 12th of October each year, this is Spain's national day. It's a national holiday that commemorates Christopher Colombus' arrival in the new world and is marked by a military parade in Madrid presided over by the Spanish king.
Traveling to Spain in October? Check out these great itineraries.
Best of Spain: Barcelona, Madrid & Seville - 7 Days. From medieval castles to some of the world's best wine, explore Spain's culture and history on this packed weeklong getaway. Not only will you get the coast, but you can also see Madrid's Fiesta Nacional parade if you're traveling during the middle of the month.
Best of Andalusia's Interior - 8 Days. This 8-day cultural tour takes you from Seville to Granada in Spain's southernmost region, Andalusia, which enjoys pleasant weather in October (great for walking tours).