This protected reserve, part of the Península de las Salinas, is 20 sq km of gray-brown sand mounds, some as high as 12m. A guided tour (in Spanish) offers views of the dunes and beaches beyond and is well worth a look if you want to see a unique landscape in the Caribbean. The brown, sandy beach nearby gets crowded at weekends and is particularly popular with windsurfers. Weekdays it's all yours.
To get to Las Salinas, take Av Máximo Gómez 400m west of Parque Duarte and turn left at the Isla gas station onto Av Fernando Deligne; this eventually bears right onto a single paved road that passes through several small ‘towns,’ at least one of which has an ATM. There’s a naval station at the end of the road; continue past the guard’s pillbox and turn left. Follow this road into town. The entrance to the dunes is 1.5km east of Salinas Hotel & Restaurant, a good accommodation option.