Boston dopers: need a spa recommendation

[Cervaise]

Specifically, for a Valentine's Day gift.

I'm in Seattle. My girlfriend is in Boston (or, rather, Somerville, to be specific). As such, I have very little practical knowledge about the area: just the small amount I've learned on a few brief visits, which does not include any sojourns to area spas.

I want to get her a gift certificate for spa services (massage, certainly; pedicure, probably; skin care, perhaps; etc), but I need opinions on good, avoid, overrated (and/or overpriced), and the like.

So, talk to me. What are some good options?