In a city where church spires spike the sky from amid a medley of medieval and modern buildings, it’s easy to pass by Magdalen Chapel with hardly a second glance. But the unassuming chapel is worth stopping for—its stained glass offers a literal window into the past.

Magdalen Chapel has the only stained glass that survived the Scottish Reformation in its original location. The building’s central window contains four stained glass shields, including one that represents the Royal Arms of Scotland and the arms of Mary of Guise, the mother of Mary Queen of Scots. The Scottish Reformation led to the destruction or removal of most religious art in favor of less extravagant decor, making this rare, colorful relic an architectural anomaly.

The chapel itself was built in 1541 for the Incorporation of Hammermen, a trade guild. In the years leading up to the Reformation, Mary of Guise, the Queen Regent, organized academic lectures within its walls. The Queen Regent, like the church, was Roman Catholic.

But the small chapel soon became a part of the Protestant Reformation. Colleagues of John Knox, a key figure in the Reformation, preached there. After the Reformation, the Hammermen appointed a Protestant minister to take the place of their Catholic chaplain. Several of Edinburgh’s Protestant martyrs were taken to Magdalen Chapel to be dressed for their burials. The table situated below the stained glass windows was utilized for this purpose. Now, the Scottish Reformation Society uses the building as its headquarters.