El Zanjón de Granados and the Casa Mínima

Right here, beneath calle Defensa, a stream once flowed. It was called the Tercero del Sur, and locals knew it as the Zanjón de Granados.

1A mansion over a stream

This block was the seventh and southernmost in Juan de Garay's 1580 plan. The stream ran down from the higher ground to the Río de la Plata, and over time it was channelled and covered. Around 1830 the mansion you see was built on top. After the yellow fever of 1871 its owners left, and the building became a conventillo, a tenement packed with dozens of immigrant families.

2The 1985 discovery

In 1985 businessman Jorge Eckstein bought the derelict house to open a restaurant. While clearing it, the floor gave way and revealed a maze of brick tunnels, cisterns and wells. He changed his plans: today it's a private archaeological museum, with around 150 metres of tunnels that once channelled the stream.

Neighbours say a spirit wanders the tunnels; that belongs to local folklore, not to archaeology.

3The Casa Mínima

Turn into Pasaje San Lorenzo. There stands the Casa Mínima, about 2.30 metres wide. Tradition says a gentleman gave this strip of land to a freed slave. No document proves it: research suggests it was part of a larger house that was divided up after the 1871 epidemic.

4What to look for

• The façade at Defensa 755, with its tall wooden doors.
• The Casa Mínima: compare its width with your outstretched arms.
• The cobbles of Pasaje San Lorenzo, one of the oldest corners of San Telmo.