gardens & ruins & otherworldly places in Spain (and France)

Madrid is likely to be quite hot in July, and Andalucía can be utterly miserable at that time of year (unless you're splashing around in water, etc.). I suggest checking historic weather data for your currently-planned Spanish destinations before committing to them. In mid-summer, I'd recommend the Pyrnees or the stretch on and near the northern coast, from the Basque Country to Galicia.

Seville's average high temperature for the month of July is 38.5 C (101.3 F).

I agree with acraven's assessment of the weather. If this is your first trip to Spain then Madrid is a must. You might want to consider instead the northern regions - Galicia, Asturias and the Basque Country (which also extends into France).

BUT.... I think you're aiming for grand gardens with a feel like Buen Retiro Park and the Alcazar and I can't think of anything that fits the bill up north. And while the Basque Country's terrain will feel like Sintra on crack, there are no Moorish ruins or colorful castles I can think of in these regions.

The titanium-clad Guggenheim Bilbao feels otherworldly but it is not a garden. It's more of a modern sculptural building with unusual installations like a 40-foot terrier made of flowers, a 30-foot bronze spider, and an hourly fog display.