From Madrid · 40.42° N · 3.70° W
Four getaways with a night away and three day trips from Madrid for 15 August, the Assumption: mountains above 1,700 metres, lakes and rivers to swim in, Consuegra Medieval and La Paloma for those who stay.
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In August Gredos is the cool sierra two hours from Madrid: on the Platform, at about 1,750 metres, you walk in temperatures ten degrees lower than in the city and the Laguna Grande can be reached without snow. In July and August the car park fills up: head for the Platform before eight.
In August Lake Sanabria is a freshwater beach, with Custa Llago, Viquiella, El Folgoso and Arenales de Vigo beside the road and cold water even in high summer. Swim only in the marked areas and go up to the mountain lagoons first thing.

July and August are swimming and kayaking season in Ruidera, with marked swimming areas and warm water. The park fills up at weekends and at midday the paths scorch: kayak early, swim in the hot hours and the cool Cueva de Montesinos in the afternoon.

In summer the Júcar is Alcalá's swimming pool: canoeing on the river or rafting on the Cabriel in the morning, and in the afternoon the caves dug into the rock, which keep cool. The sunny slopes are tiring in the height of August: the old town and the castle, first thing or at dusk.

In August the Cotos pass, at over 1,800 metres, is about ten degrees cooler than Madrid, and the Zabala route to the Laguna Grande is walked in the long summer light. Some streams are dry, but the lagoon is not: get to Cotos before nine, as it fills up.

In mid-August Consuegra Medieval, a Festival of Regional Tourist Interest, re-enacts the battle of 1097 over several days at the Muela castle, with a market, living chess and some two hundred locals in period dress. The road of the windmills is closed and the castle changes its prices: check the programme.

For those who stay: around 15 August La Latina celebrates the Virgen de la Paloma, the biggest of the castizo street festivals, with chotis dancing, free concerts and the firefighters bringing the painting down. The last two hours at the Prado are free and air-conditioned; the Retiro boat, at sunset.
Questions
Yes, the Assumption is a national holiday. When it falls on a Sunday, the Community of Madrid has moved it to the Monday in other years: check the working calendar.
In the Ruidera lagoons, less than three hours away, in the Júcar at Alcalá del Júcar and in Lake Sanabria, further away. Always swim in the marked areas.
The fiestas of the Virgen de la Paloma in La Latina, with street dances and free concerts, which close those of San Cayetano and San Lorenzo.
Yes, without snow. Set off before eight from the Platform car park and come down before the afternoon storms.
Geocaliahttps://www.geocalia.com/en/spain/community-of-madrid/madrid/getaways/august-long-weekend