A Monumental City
by acemj
At every square, there is seemingly some sort of monument, statue or piece of art. This equestrian statue in the Puerta del Sol and you'll find many more by just strolling around the city. Incidentally, Puerta del Sol is considered "ground zero" for the entire country and you can find a marker in the square which indicates the spot from which all official distances are measured. It is also a hub for public transportation and shopping and a great central meeting spot to begin your exploration of the city.
Tapas
by andal13
Probably most interesting typical custom is "ir de tapas". What does it mean? With friends (better) or alone, you go to a bar and have a drink; may be a "caña" (beer), a cup of wine, a cocktail or a soda. The drink comes with little dishes called "tapas" (olives, ham, peanuts, "tortilla"...) and some places are famous for their dishes, so you must go for one bar to the other!
Probablemente, la costumbre típica más interesante sea "ir de tapas". ¿Qué significa? Con amigos (mejor) o solo, vas a un bar y tomas algo; puede ser una "caña" (cerveza), una copa de vino, un cóctel o un refresco. La bebida viene con unos platitos llamados "tapas" (aceitunas, jamón, maníes, tortilla...) y algunos sitios son famosos por sus platos, por lo que debes ir de un bar a otro!
Manzanares
by el_ruso
If you have time I urge you to visit this place. It is about 30 min by bus from Madrid's Cuatro Caminos bus station, and buses leave every 30 min.
The castle is simply fantastic and looks like it belong in a fairy tale. Yet it is real and historic XV century stronghold. If you are in Spain you have to see at least one castle, and this one is among the best preserved and most beautiful. Also it is the closest castle to Madrid I believe.
The mountains behind it are awesome and add to the scenery.
Salamanca
by el_ruso about Fashion
Area North and East of Parque El Retiro is where the upper classes reside. It is called Salamanca. (Do not confuse with a city of the same name.)
There are many stores where your girlfriend or wife could buy stuff for a surprisingly reasonable price. Stores belong mainly to Spanish designers: Mango, Sfera, Berushka (or something close to that), and they are both fashionable and reasonably priced.
Alternatively, you can go to a department store. The main one is called Corte Ingles and its main store is located on Puerta del Sol square. But prices there are going to be a lot higher.
Flamenco
by LanaFromRiga about Flamenco
Flamenco started in Andalusia, but flamenco in Madrid is in high level dancing art too. Professional cante flameco with guitar sounds in the “Casa Patas” club (Calle de Canisares 10). Tablao reputation has “Café – de - Chinitas” (Calle Torija 7) where you can see flamenco dancing.