In 1385, João I vowed on the plains of Aljubarrota that if his underequipped and outnumbered army defeated the invading Castilians, he would commemorate his spiritual indebtedness to the Virgin Mary. The result is the magnificent Monastery of the Virgin Mary, designed in splendid Gothic and Manueline style.

The western porch, ornamented by a tangled mass of Gothic sculpture of saints and other figures, sits beneath stained-glass windows of blue, mauve, and amber. The windows are exceptionally beautiful and are best enjoyed on a sunny day. Because the windows were damaged over the centuries, various artisans have replaced them in their original 16th-century Manueline detail.

In the Founder's Chapel, João I and his English queen, Philippa of Lancaster (daughter of John of Gaunt), lie in peaceful repose, their hands entwined on their stone effigies beneath an exquisite octagonal lantern. Prince Henry the Navigator's tomb is near that of his parents. His fame eclipsed theirs even though he never sat on the throne. The Royal Cloisters reveal the beginnings of the nautically oriented Manueline architecture.

The magnum opus of the monastery is the Chapter House, a square chamber whose vaulting is an unparalleled example of the Gothic style, bare of supporting pillars.

Sentinels and the glow of an eternal flame guard the two tombs of Portugal's Unknown Soldiers from World War I. In one part of the quadrangle is the Unknown Soldiers Museum, which houses gifts to the fallen warriors from the people of Portugal and other countries. Beyond the crypt are the remains of the old wine cellars. You can visit the crypts daily from 9am to 5pm, but you might not want to unless you're a crypt aficionado. These consist of a series of dank and gloomy ancient tombs, but no notable treasures.

Stunning filigree designs ornament the coral-stone entrance to the seven unfinished chapels. The capelas, under a "sky ceiling," are part of one of the finest examples of the Manueline style, a true stone extravaganza. Construction was abandoned so workers for Manuel I could help build his monastery at Belém.