The Pampas are famously flat, which is why the Sierra de la Ventana looks so improbable, a long wall of quartzite ridges erupting from the grassland in the south of Buenos Aires province. Cerro de la Ventana is the one with the hole in it. Near the crest, at a little over a thousand metres, erosion has punched a natural window through the rock, and on a clear day from the plain you can see the sky through it like a small bright coin. The trail to it takes a few hours of steady uphill walking, and it is a rite of passage for people from Bahía Blanca and the capital.
Charles Darwin climbed one of these hills in 1833 during the Beagle's voyage, and wrote about the odd contrast of the rough quartz crags with the endless plain around them. The ranges here, the Sierras Australes, are among the oldest in Argentina, and their rock was folded and worn down hundreds of millions of years ago. The air is dry and clean, the light on the ridges in the late afternoon is a copper colour, and the grass around the foothills smells of thyme and dust.
For a rider coming from the flat country, the first thing to notice is the wind. It blows steadily across the plain, and it can lean a bike over on the long straight roads that lead to the hills. Routes 76 and 72 run through small farming towns, with gravel side roads that wander toward the sierra, and the sealed roads are generally quiet. Cattle and horses graze beside the fences, and occasionally a rhea runs along the verge. Gravel surfaces can be loose and unforgiving, so take care and keep the speed down.
The town of Sierra de la Ventana, a short distance east, is the base for visitors, with cabins, a few restaurants, a bakery and a station on the old railway. The best seasons are spring and autumn, when the days are mild and the grass is green. Summer afternoons can be hot, and winter brings frost and sometimes snow on the peaks.
Argentine meat is the obvious lunch, and a roadside parrilla with a plate of beef and a glass of red is a fine way to finish the day.