More history is packed into this single block of buildings southwest of Plaza de Mayo than in scores of other city blocks put together. Its name, which literally means "the Block of Lights," is a metaphorical nod to the "illuminated" scholars who once worked within. Most of the site can be visited only on guided tours led by excellent professional historians. Regular departures are in Spanish, but they provide brochures with English summaries of each stage.
The earliest occupant of the site was the controversial Jesuit order, which began construction here in 1661. The only survivor from this first stage is the galleried Procuraduría, the colonial administrative headquarters for the Jesuits' vast land holdings in northeastern Argentina and Paraguay (think: The Mission). Secret tunnels, still undergoing archaeological excavation, linked it to area churches, the Cabildo, and the port. Guided visits include a glimpse of a specially reinforced section. After the Jesuits'
expulsion from Argentina in 1767 (the Spanish crown saw them as a threat), the simple brick-and-mud structure housed the city's first school of medicine and then the University of Buenos Aires. Fully restored, it's now home to a school for stringed instrument makers and a rather tacky crafts market.
The Jesuits honored their patron saint at the Iglesia de San Ignacio de Loyola (Church of Saint Ignatius of Loyola), at the intersection of Alsina and Bolívar. It's the only building in the block you can visit without going on a tour. The original sanctuary here was built of adobe in 1675; within a few decades it was rebuilt in stone.
Argentina's first congress convened within another building on the site, the Casas Virreinales (Viceroyal Residences)—ironic, given that it was built to house colonial civil servants. The remaining historic building is the neoclassical Colegio Nacional, a top-notch public school and a hotbed of political activism that replaced a Jesuit-built structure. The president often attends graduation ceremonies, and Einstein gave a lecture here in 1925.