Been to Spain? Madrid or Barcelona (Singapore)

I'm planning to visit Spain in October for 3 weeks and wanna hear from those who are from Spain or been there.

I'm into Architecture and Arts (mainly old masters and theatre etc), i'm looking to enroll in a local language school for a week or 2 to brush up my spanish.

1) Madrid or Barcelona (or any others like Granada or Seville etc) and which area to stay?
2) Any local language school to recommend?
3) How safe is it for me to go alone?
4) Any nice restaurants or cafe to recommend?

Cheers,
Rhyssie