South of the Santa Cruz–Quijarro railway line, the tropical dry forest gradually gives way to the Chaco, a vast and arid landscape of dense scrub and virtually impenetrable thornbrush stretching south to the Paraguayan border and far beyond. Inhabited only by isolated cattle ranchers and occasional communities of Guaraní and semi-nomadic Ayoreo, the Chaco is one of South America’s last great wildernesses and supports plenty of wildlife – much of it now protected by the Parque Nacional Kaa-Iya del Gran Chaco, which covers over 34,000 square kilometres southeast of Santa Cruz adjacent to the Paraguayan border. However, there are few organized tourist facilities in the Chaco, and unless you hire your own 4WD, your view of the region will be limited to what you can see from the window of a bus or train. The region’s main towns are Villamontes, the Bolivian Chaco’s biggest settlement, and Yacuiba, on the Argentine border. Adventurous travellers can also take the strenuous trans-Chaco road, which heads east to the Paraguayan border at Fortin Villazón, and then onto the Paraguayan capital, Asunción.