se mettre au vert

To go stay in the countryside for a break

About swapping the city for some peace and quiet, though it can also mean lying low out of sight.

Après cette année épuisante, ils ont décidé de se mettre au vert pendant quelques semaines.

After such an exhausting year, they decided to head off to the countryside for a few weeks.

'Vert' meant pasture as far back as the 16th century, and for a long time the phrase was just about putting a horse out to graze, as La Fontaine does in one of his fables. It only shifted to mean a person taking a rest in the countryside around the middle of the 19th century, and later picked up its underworld sense of lying low.