The Fantastic Playgrounds of Spain: Parque Infantil del Parque del Oeste

A nice little playground next to the Teleférico stop in Parque del Oeste. Madrid has really improved this playground since the winter, they turned half of it into a rubberized play surface, leaving the other half sandy-sandy sand. It has a kid-propelled carousel, swings, this cool spider web thing, and other things. Features amazing views of Pozuelo del Alarcón. There are telescopes that work with 1 euro coins near the playground. 

Logistics: Argüelles metro stop is up the hill...or you can take the Teleférico! Yes that is right, this playground is right next to the Teléferico stop (Estación de Rosales).* If that's not enough playground for your kid, you can keep walking (or scooting) along the lovely wide paseo overlooking Parque del Oeste and reach the Templo Debod playground, which is very similar (has similar equipment) and is very sandy.

Notes: If you can get over the grossness of the playground being, essentially, a giant sandbox, you can bring buckets and shovels to build sand castles (get the water from nearby public fountains).

*if you like heights and shakey rides high above the earth, you can take the approximately 11 minute cable car ride to Casa del Campo. There is a nice terraced restaurant at the other end of the Teleférico that is sort of a Chiringuito-style Chuck E. Cheese in the city (think astrotruf, play structures, skee ball, and beer served in paper cups. Disclaimer: I haven't been there in years , but in the pre-parenting days it seemed like a fun-enough place full of tired parents and children running wild.)