Olivia Culpo Rocks Red Bikini on Boat in Spain with Danny Amendola

Olivia Culpo and Danny Amendola are vacationing in Spain together ... and when we say the views are spectacular, we ain't talkin' the Torre de Savinar.

The on-again, off-again couple are getting some quality time on the Spanish islands this week ... but Olivia ditched the dudes for an all-girl yacht trip with friends.

So, what are they up to? Taking lots of photos of each other in sexy poses ... and for good reason, they're all insanely hot models.

As for Amendola, the two were spotted at dinner together the other night -- not the greatest body language -- but couply enough.

At least his tan looks great!

Remember, the two broke up back in March after dating for 2 years -- but they started hanging out again at a friend's wedding earlier this month ... and now, boom -- European vacation.

Totally back together, right?