Villa Unión

Locally:

The Viewpoint
northeast of city center
Miguel Angel Gaitán
a mummified child in the cemetary, believed to deliver miracles
The Dam
as tempting as it is in the heat, swimming here is not allowed
Banda Florida
west of town. Beautiful rock formations, ancient petroglyphs in the rocks
Anchumbil
east of town. Similar to Banda Florida.

Nearby:

Talampaya National Park
Pre-historic, massive, intensively red canyons. (http://www.talampaya.gov.ar)
Laguna Brava
A beautiful lake in the high altitudes, with flamengoes and more fauna.
Guandacol
El Chiflón
Ischigualasto National Park
also called "Valle de la Luna"