The Madrid Metro comprises 12 lines extending to 283 stations across 284 km of track, with a ridership of 3.4 million per day.
Fare: 1 Euro with metro card
Hours: 6 AM - 1:30 AM
Madrid's subway is one of the world's densest, having expanded at Asian speeds (50km in six years) to an especially large scale given Madrid's relatively small size (around 3.5 to 6 million). In addition to fast, reliable, and frequent rides, the subway features stations that run the gamut from quaint to spacious to sexy. Newer stations include natural-like lighting and ample entryways. The system also boasts environmentally friendly cleaning -- and one of the coolest subway ad campaigns we've seen.
Flickr: felipe gabaldon; caravinagre