Arequipa's serene Convent of Santa Catalina, founded in 1579 under the Dominican order, is the most important and impressive religious monument in Peru. The 16th-century convent remained a mysterious world unto itself until 1972, when local authorities forced the sisters to install modern infrastructure, a requirement that led to opening the convent for tourism. Today only 19 cloistered nuns, ages 20 to 90 remain, mostly out of sight of the hundreds of tourists who arrive daily to explore the huge and curious complex. Although the nuns, all from wealthy Spanish families, entered the convent having taken vows of poverty, in the early days they lived in relative luxury, having paid a dowry to live the monastic life amid servants (who outnumbered the nuns), well-equipped kitchens, and art collections.

Behind tall, thick sillar fortifications are walls painted sunburned orange, cobalt blue, and brick red, hiding dozens of small cells where more than 200 sequestered nuns once lived. Santa Catalina is a small, labyrinthine village, with narrow cobblestone streets, plant-lined passageways, and pretty plazas, fountains, chapels, and secret niches and quiet corners. Not by accident does it look and feel like a small village in southern Spain, with its predominantly mudéjar (Moorish-Christian) architecture and streets named for Spanish cities. In all, it contains 3 cloisters, 6 streets, 80 housing units, an art gallery, and a cemetery. The interplay of intense sunlight and shadows, tiny white-stone windows suddenly framing brilliant bursts of color, and sense of splendid isolation from the city beyond make for an incredible aesthetic experience. No less an expert than the great Portuguese architect Alvaro Siza called Santa Catalina a "magnificent lesson in architecture." Yet, alarmingly it is on World Monuments Watch list of Most Endangered Monuments; experts say the great convent is threatened by structural damage caused by pollution and earthquakes.

Among the convent's highlights are the Orange Tree Cloister, with mural paintings over the arches; Calle Toledo, a long boulevard with a communal lavandería at its end, where the sisters washed their clothes in halved earthenware jugs; the 17th-century kitchen with charred walls; and the rooms belonging to Sor Ana, a 17th-century nun at the convent who was beatified by Pope John Paul II. Visitors can enter the choir room of the church, but it's difficult to get a good look at the main chapel and its marvelous painted cupola. To see the church, slip in during early morning Mass (daily at 7:30am); the cloistered nuns remain at the back, in view behind a wooden grille. Visitors are advised to take an informative guided tour (in English and other languages, available for a tip of about S/20), though it's also fun just to wander idly around discovering its myriad spaces, especially before or after the crowds arrive. For an especially transfixing experience, visit at night, when cells and the huge kitchen are illuminated by wood fires and flickering candles (come in the early evening as the sun sets). Allow at least a couple of hours to see the convent in all its glory.