The first settlement here, at the end of the 18th century, was called Arraial Velho - "old settlement" - and it fell into ruin almost immediately. The site, on the banks of what is now the São Domingos River, was not easy ground to hold. In 1821 two Portuguese men, Domingos and José Valente, arrived hunting for gold. They brought with them an image of São Domingos Gusmão - Saint Dominic of Caleruega, the 13th-century Spanish friar who founded the Dominican Order. The saint's name attached itself to the settlement and to the river that ran past it: São Domingos. The town grew slowly through the next decade as more Portuguese settlers arrived. In 1835 it became a district of Arraias - a neighboring town that is now part of Tocantins state - and in 1854 São Domingos became a municipality in its own right. That date places it among the oldest municipalities in Goiás, predating most of the region's settlements by decades. But oldness did not bring wealth. São Domingos has remained, through every subsequent census, one of the poorest towns in the state.

São Domingos sits at the edge of the Serra Geral, the great escarpment that forms the northeastern boundary of the central plateau. The municipal seat is mountainous on most sides, and the air is humid tropical, with an average annual temperature of 26 degrees Celsius. The cerrado here holds some of Brazil's most prized hardwoods: cedar, aroeira, ipê, peroba, braúna, vinhático, umburana. The pequi tree, the buriti palm, and other iconic cerrado species define the local vegetation. To the east lies Bahia. To the west, Iaciara. To the north, Divinópolis de Goiás. To the south, Guarani de Goiás. None of these towns are close to any major highway, and the closest section of the federal network runs through Alvorada do Norte, another municipality that had to work to get itself placed on a map. São Domingos's 128,000 hectares of farmland are divided across 763 farms. The primary crop is corn, planted on 4,500 hectares. The cattle herd numbered 144,700 in 2006 - a large figure for a place so thinly populated.

The real treasure of São Domingos is underground. Parque Estadual da Terra Ronca protects one of the largest cave systems in Brazil, centered on two major caverns: Terra Ronca itself, which gives the park its name, and the Angelica cavern, whose explored passages extend for 14 kilometers - among the longest in the country. Terra Ronca produces its roar because of an underground river that flows through limestone passages, echoing through chambers and fissures until the sound emerges at the mouth as a low, continuous hum. Bats nest in some of the passages. Speleologists continue to map new sections. The park is named for the cave, the cave is named for the sound, and the sound is ancient - pre-human, older than the settlement that came to listen to it. The landscape above is equally striking, with karst formations visible for miles where the limestone bedrock has weathered into cliffs and spires. It is one of the reasons filmmakers come: a TV miniseries called Grande Sertão Veredas, adapted from João Guimarães Rosa's novel, was filmed in the region.

São Domingos is further from Goiânia than any other Goiás municipality - 641 kilometers - and the road to get there is a chain of connections: BR-153 to Anápolis, then BR-060, then several smaller state highways, ending with 64 kilometers of unpaved road. That distance has kept the municipality poor. In 2000 the Human Development Index stood at 0.631, ranking São Domingos 239th out of 242 municipalities in Goiás - nearly at the state's bottom. The adult literacy rate was 74 percent against a national average of 86.4. The infant mortality rate of 41.97 exceeded the national average of 33. One hospital serves 10,996 residents. The 17 schools, with 3,291 students, struggle with the same resource constraints that define rural northeastern Goiás. The economy rests on subsistence agriculture and cattle raising. Almost none of it is based on tourism, despite the cavern that made the park famous.

The contrast defines São Domingos. Aboveground, a small and underfunded town that shares the name of a Portuguese saint. Below ground, one of the most spectacular cave systems in Brazil, with an underground river that has been roaring through limestone since long before any settlement existed to hear it. The founders were prospectors who came for gold and stayed for land. Their descendants are ranchers and farmers, in a place that has stayed small because it is hard to reach and hard to leave. Meanwhile the park protects something older than any of it - Terra Ronca, the roaring earth, doing exactly what it was doing when the first Portuguese settler asked a local what the sound was, and was answered in a word that became the cavern's name, and then the park's name, and now, in a circuitous way, the name of São Domingos's best-known attraction.