Check weather stats for the northern regions at wunderground.com

Northern Spain including lovely cities like San Sebastian and Santander .

Ditto the above.. San Seb is wonderful..Look at You Tube to get an idea..Don't know Santander but you can see lots on You tube to point out special spots.

... and the Asturian and Galician coasts. Oviedo's worth a visit too, as is Santiago de Compestela. As Yorkshire says, check the temperatures at wunderground.

San Sebastián is a good bet both for the fantastic food, the climate (the Spanish go up to this coast in summer to escape the heat), the landscapes, the beaches etc etc. http://travel.nytimes.com/2011/08/07/travel/36-hours-in-san-sebastin-spain.html?_r=0

European Capital of Culture 2016, video presentation: http://www.youtube.com/watch?v=PUdOeA0GeEg

Surprised no-one has mentioned Bilbao, a great city with similarly great pinxtos. It has a rougher Basque edge to it than San Seb, that can be a plus or minus depending on your point of view. It will also have the cooler weather you are after.

Madrid and anywhere south of it is an absolute no-go in July and August.

Bilbao is great too, I have often had to go there every now and then for a change of air when the prettiness of San Sebastián just becomes too much. Two fabulous and very different sister cities.

I'm always amazed at the amount of ill-conceived, thoughtless advice people are so ready to spew in this forum. All these responses are just mindless reactions given with zero thought. Further north is cooler. Why not actually try to think about where and how the temperature varies.

First, your question is to vague to answer. There is a big difference between June and August. Heat isn't so much of an issue in June, but would be in August. But you don't say when you are going. You also don't say what you mean by hot. 90 is hot for some people and not for others.

Second, there is a big difference between inland and coast. A city like Barcelona won't get really hot. Sevilla will.

Third is elevation. Madrid is high, so it doesn't get that hot even in summer.

I suppose that you could have simply gone to one of the weather sites and checked monthly temperatures in various places, but then you would actually have to do work instead of having other people spoon feed you just like mommy used to do.

So you're saying Madrid doesn't get hot in the summer?

I think the north coast is nice.

Madrid does get hot in summer by any normal sense of the word, in the 90s Farenheit in July and August, although rarely over 100 (or 40 C). Madrid isn't that high as to avoid being hot due to its location in the south, although it is dry. It's less than half the altitude of Denver, for example.

Madrid can indeed be a furnace in summer, but frankly I've still enjoyed the city during that time. At least its not humid.

We spent a month in Catalonia (the Dali triangle) in August, including Barcelona, several villages near Girona, the Costa Brava (Cadaques) and the Pyrenees bordering France. It was hot, but not unbearable.

My goodness, there are some very nasty people replying-- regardless of temperature fluctuations, perhaps San Sebastian, Bilbao, and my #1 pick, Barcelona. Check for AC at hotels of course.

How is Santiago de Compostela in the summer?

weber,

I've been to Santiago 4 times during the summer (July/ August). Temps have been in the
70's, even 80 during the day and then cools at night, very pleasant. There's always been a day or two of some rain.

Many Madrileños go to San Sebastiam, Zarautz etc to escape the heat, Barcelonans go to the Costa Brava and the Catalan Pyrenees to escape Barcelona's humidity which is unpleasanteven if temperatures are not particularly high.
Northern Spain meaning the autonomous communities on the Atlantic coast (Galicia, Asturias, Cantabria, Euskadi)is generally cooler; obviously northern Spain inland, eg Castilla y Leon and Navarra is also hot (we had 40ºC at 9pm in Plamplona last August!)