Córdoba contains one of the most extraordinary buildings in the world — the Mezquita-Catedral, a Great Mosque built by Abd al-Rahman I from 785 AD and expanded over three subsequent centuries into a forest of 856 columns under which a Christian cathedral was controversially built in the 16th century at the express command of Charles V (who, on seeing the result, reportedly said "You have destroyed something unique to build something ordinary"). The tension between these two sacred buildings in a single structure is the defining fact of Córdoba, a city that was once the largest in Europe and the intellectual capital of the Islamic West. The Judería (Jewish quarter) alongside is among the finest preserved medieval Jewish urban environments on the continent.
From London and several UK airports it's just over two hours to Seville or Málaga, then 45 minutes by AVE high-speed train (€15) or bus. There are no direct flights to Córdoba but the train connections make it easily combined with Seville (45 minutes away). Go from March to May — the spring patio festivals (the Fiesta de los Patios, UNESCO Intangible Heritage) open the private flowered courtyards of the Judería to the public in May, and the temperatures are perfect. September and October are excellent. June to August is extremely hot (Córdoba is the hottest city in Spain).