Spring
Spring in Seville is the walking season before the dry heat takes over. March, April and May are for towns, trails and days outside that are not yet a sea-only brief. The water is not the whole point, even when the sky looks like a holiday.
In Seville the meteorological summer is June, July and August and winter is December, January and February. Pack a layer for mornings. The interior, if you leave the obvious strip, lags the coast. This is the window where Seville is pleasant without the high-season crush.

