Where to stay
We have not held rooms anywhere, so book your own, a hotel or an Airbnb. These are the two areas that make sense.
Boadilla del Monte
Next to the venue
The easy option: a very short ride home, or a walk, and nobody has to worry about getting back late. It is a quiet town with few beds, so they go early.
Madrid
Half an hour by car
Better if you want to make a weekend of it. Anything you like at any price, and it leaves you Sunday to see the city.
Book early. The wedding is on a Saturday and 12 October is a national holiday in Spain, so Madrid fills up that weekend and prices climb the longer you leave it.