The Barcelona subway grinds to a halt, the doors slide open and commuters pour out to go about their daily business. Little do they know that as they do so, a burst of energy is sent up to street ...

Driving is not recommended. Diamond-shaped signs wearing an "M" mark the locations of Barcelona's Metro stations. This underground rail system serves much of the city on eight color-coded lines.

The Barcelona subway grinds to a halt, the doors slide open and commuters pour out to go about their daily business. Little ...