Strolling along the arcaded Ljubljana Central Market and the adjacent outdoor market that fills Pogačarjev Square with stands protected by green and white awnings, I was happily purchasing honey from local apiarists and unique glassware. As droplets of spring rain began to fall from a steely sky, the massive church right next to me beckoned me, offering shelter and an amazing collection of visual stimuli.

Built between 1701 and 1708 to Baroque designs by a Jesuit architect, the Cathedral of St. Nicholas has seen decades of additions ever since, but it retains a harmonious cohesiveness. I started at the main entrance and looked up at the pair of twin bell towers, sporting eight clock faces and holding six bells, including the second-oldest bell in the country, dating from 1326. But it’s the feature at eye level that garners lots of attention. I was staring at one of the top five doors in the world. A pair of bronze doors, named the Slovene Door, was added only in 1996 to celebrate the coinciding 1,250th anniversary of Christianity in Slovenia and a visit by Pope John Paul II. Sculptures portraying the national history of Slovenia cover the doors, including, at the very top, the pope peering down from a window at such scenes as the Crusades and the independence of Slovenia in 1991. The most curious aspect of the door is its lack of a handle or doorknob. Worshippers gain access to this outstanding house of worship by tugging on part of the sculpture itself, giving it the appearance of burnished gold after more than two decades of human hands opening this door.

I circled around the church. The subdued and mercurial façade — a soft putty color on a cloudy day, more yellow when it’s sunny, and nearly salmon during sunset — features some sandstone statues of saints and bishops standing in wall niches (added between 1872 and 1913), elliptical windows, a couple of frescoes, and a sundial, from 1826, with Roman numerals and a cautionary Latin motto that translates as, “You don’t know the date or the hour.” To the left of the sundial, I came upon another remarkable pair of doors. This set, called the Ljubljana Door, depicts the history of the Ljubljana diocese, with six sculpted 20th-century Ljubljana bishops wearing mitres and standing above the enshrouded body of Christ.

I passed through this door and entered the cathedral, immediately awed by the grandeur that the subtle exterior belies. None of the nine daily Masses was being celebrated, so I had free reign to roam around and take in all the outstanding features at my leisure. The walls of the half dozen side chapels are slathered in frescoes and paintings from the 1700s, and the black and white checkerboard floor of the central aisle leads past beautiful marble Corinthian pilasters to an altar that was added in 1774. Above the altar painting of the Adoration of the Magi, a dozen small angels float around an organic light fixture, like a vine sprouting slender candles. Statues of four bishops occupy the niches under the octagonal dome over the crossing between the nave and the transept. The dome, added in 1841, replaced a fake one that was simply painted on the arch, and the frescoes on its cupola (portraying the Holy Spirit and angels) and walls (depicting the coronation of the Virgin Mary and the glorification of St. Nicholas) didn’t show up until a few years after that.

At the opposite end of the church, the organ loft is a Baroque masterpiece, with organ pipes surrounded by golden angels and cherubs playing brass and string instruments. The cathedral’s piece de resistance stretched out far above me. Created by the Italian artist Guilio Quaglio, a tremendous ceiling painting shows the transfiguration of St. Nicholas that covers the vault of the nave. Around the edges, Christians are being persecuted under emperors Nero and Diocletian amid angels, apostles, and other figures in various costumes and poses, some toppling out of false frames and others leaning against fake architectural elements, some at their exact moment of a violent death. With a series of clever features, including two false domes, Quaglio achieved such wonderful illusionist effects that you’ll be hard pressed to differentiate between reality and the imaginary. You may end up with a crick in your neck from staring up at Quaglio’s masterpiece, but the discomfort will be well worth it.