[Arcten]

I spent 4 months travelling throughout Spanish South America and some of my favorite cities where I would consider being a nomad were Buenos Aires, Montevideo, Medellín, and Valparaíso.

All have good night-life, art, and excepting Medellín are on the ocean.

Montevideo has easy access to world-class beaches and is only a couple hours by ferry from Buenos Aires.

Valparaíso is an hour or so by bus from Santiago if you're interested in having a big city nearby.

As far as learning Spanish, it'd be much cheaper in Colombia, but you'll be able to find classes in any of those places. Argentinian Spanish is known for an odd accent and some different grammar, but it's nothing terribly different.