From Madrid · 40.42° N · 3.70° W
Seven getaways of one or two nights and two day trips from Madrid, chosen for what is open or on stage over the December long weekend: snow if there is any, theatre in Almagro, Gregorian chant in Silos and stone villages.
Map
The Casa del Parque and the tourist office are also open on 7 and 8 December. In winter it may snow on the Peña de Francia, and with snow you cannot walk up. On a long weekend, book accommodation and meals in good time.

Valdesquí is open from December to April depending on the snow, so early in the month there may be none: check the report the night before. If it has snowed, book the car park free of charge and bring chains, which the M-601 requires. If not, the Camino Schmid and Fuenfría.
The Visigothic hermitage of Quintanilla de las Viñas opens specially on 7 December, and the Fernán González tower on the 7th and 8th. In Silos, vespers at 19:00 every day. San Olav, on the other hand, is closed in December.

In winter the cathedral is open on Saturdays and public holidays until 19:30, and the Museum of Abstract Art, in the Hanging Houses, has an exhibition of Yves Klein. The Serranía often freezes: boots for the Ciudad Encantada, or the Paleontological Museum if there is ice.

Canoeing runs all year depending on the weather and bookings, and the lamb at El Panadero has to be ordered when you book. The Casa del Parque is closed on Tuesdays and Wednesdays: if your long weekend falls on those days, call in on the first one.
In winter the Casita del Príncipe opens only on Saturdays and public holidays, and has few places: buy your pass beforehand. The monastery is closed on Mondays and last entry is at 16:45; in the hills there may be snow up high, on Abantos.
The Cervantes Train usually closes its autumn season on this long weekend, and its ticket is valid for the return the next day. Alcalá schedules visits to Complutum on those days, by registration, and Cervantes's birthplace has theatrical shows on Saturdays.

The Corral de Comedias stages classical theatre over the December long weekend: La dama boba on the 6th, Don Gil de las calzas verdes on the 7th and No hay burlas con el amor on the 8th. The dramatised tour runs until the 8th. Cold nights: bring a coat.

On 8 December the cathedral opens from 14:00 to 18:30, like a Sunday, so the order of the plan works that day too; on the 6th, the Sephardic Museum is free. Buy the cathedral with a timed ticket: by half past five it is already dark.
Questions
Only if it has snowed. The Valdesquí season runs from December to April depending on the snow, and early in the month there may be no pistes open. Check the report the night before and have a plan for without snow.
The hermitage of Quintanilla de las Viñas, near Covarrubias, opens specially on 7 December; the Fernán González tower on the 7th and 8th; and the Casa del Parque in La Alberca, also on the 7th and 8th.
Alcalá de Henares by Cercanías, El Escorial by bus from Moncloa, Toledo by Avant and Cuenca by AVE for the old town. For the snow, bus 691 from Moncloa to Valdesquí.
Accommodation, yes, especially in small villages like La Alberca, Silos or Sepúlveda. Also Toledo cathedral with a timed ticket, the Casita del Príncipe and the Almagro performances.
Geocaliahttps://www.geocalia.com/en/spain/community-of-madrid/madrid/getaways/december-long-weekend