This protected area, 12km south of Santa Cruz, is a strange and striking sandy desert that seems out of place in Santa Cruz's humid environs. It's a good spot for bird-watching and you may also see sloths. The best way to visit the dunes is on a half-day trip with a Santa Cruz tour company such as Nick's Adventures, which include sandboarding. Bring sunscreen and water.
From Santa Cruz city center, bus 21 (B$2, 45 minutes) can drop you at the park entrance, from where it's a long, hot 7km walk to the dunes. It's also possible to come by taxi (about B$200), but unless you have a 4WD you will need to walk about 4km to reach the sand.