The Mediterranean summer has become unpredictable in a way it was not twenty years ago. Peak July and August now routinely deliver heatwaves in the mid-40s Celsius in southern Spain, Italy and Greece. The traditional 'visit in July' advice that dominated travel writing for decades is quietly being replaced.
Our current recommendation is to travel in May, June, and mid-September. The weather is warm but not hostile, the crowds are thinner, the prices are lower, and you can still walk through a city at 2 PM without planning your route between air-conditioned spaces.
For summer itself, we prefer neighborhoods that have meaningful shade, proximity to water, and strong evening life. Examples: Trastevere in Rome (shade, river, evening aperitivos), Gràcia in Barcelona (trees, smaller plazas, elevation), Alfama in Lisbon (coastal breeze and miradouros), Vedado in Havana (grid of tree-lined streets).
Neighborhoods to avoid in mid-summer heat: Seville's tourist core, central Athens, Naples' Quartieri Spagnoli (beautiful but a heat trap), Madrid's Sol. These places are wonderful in May and October. In August they can be genuinely dangerous.