Santa Ana to San Francisco

Take a truffi from Humahuaca to Santa Ana, a traditional empty town of adobe buildings enclosed by breathtaking mountains standing at 5,000 m.
From there, you can trek the 5 hours through spectacular surroundings to arrive in Valle/Paseo Colorado, a beautiful tiny town, and another 10 hours trek through Valle Grande to San Francisco where you'll find natural thermal baths and los yungas. It is only a two- or three-hour trek away, but beware of the elevation on your return. This two-hour trek could take up to five hours on return.
Check out the trail on OpenStreetMap (used by mobile apps like OsmAnd or Mapy.cz).