If you haven’t been to Palazzo Farnese for its once-in-a-blue-moon opening to the public yet, then go — by April 27.

Here’s why: The palazzo is an architectural gem, designed in the 16th century by Antonio da Sangallo, Giacomo della Porta, and that guy everyone’s heard of, Michelangelo. It’s a treasure trove of art, including Annibale Carracci’s world-famous frescoes of romping gods and goddesses (pictured above — since no photos were allowed in the exhibition, courtesy of the Web Gallery of Art).

And Palazzo Farnese is a key piece of juicy Renaissance history: It was built by Alessandro Farnese (later Pope Paul III) after he got his start in the Church thanks to his sister, Giulia. Why was she so influential? Well, she was sleeping with Pope Alexander VI. That helps.

Did I mention the travesty fact that this lovely papal palazzo is closed to the public? Since 1874, it’s been the home of the French Embassy. That means you can’t just wander in off the street. Unfortunately.

Now, you can… or almost.

Since December, Palazzo Farnese has hosted an exhibit titled, quite simply, “Mostra Palazzo Farnese.” Because that’s exactly what it is: a rare display of the palazzo’s gems, not least of all its rooms and galleries themselves. The gorgeous courtyard alone boasts ancient sarcophagi and sculptures, many on loan from the Naples Archaeological Museum; for those who can’t get to Naples, the exhibit also has copies of the fabulous Farnese Hercules and Farnese Bull, both just too big to be moved. (Darn them for being so impressive!)

My favorite? The Venus Kallipygos, a 1st-century B.C. marble (based on a 3rd-century B.C. Greek bronze), as much because I get a kick out of its name — literally, “Venus of the beautiful buttocks” — as because it is, well, beautiful. From top to, er, bottom.

That’s not to mention the glittering tapestries, Renaissance paintings and portraits of the Farnese family that make up the rest of the exhibition.

As far as rooms go, though, there’s nothing quite like the salon frescoed by Annibale Carracci, the famous High Renaissance painter from Bologna. Now, his frescoes are little-recognized compared to, say, those by Raphael or Michelangelo in the Vatican, but that’s a shame: Art historians always have considered them an incredible blend of both styles, and they’re usually seen as the best frescoes of the High Renaissance. What Raphael lacked in power, muscularity and dynamism, Carracci’s got. And what Michelangelo didn’t quite grasp in terms of harmony, beauty, and elegance, well, Carracci’s covered that part, too.

Don’t believe me? Just check out this image (courtesy of the Web Gallery of Art):

Here’s a close-up of that great fresco you see at the far end, the Cyclops Polyphemus:

Pretty great stuff. But if you don’t get your bottom there before April 27, there’s no guarantee you’ll get a chance to see any of this again.

The cost of the exhibit, which includes a (unsurprisingly dry, but informative) audioguide, is €12, plus reductions. Don’t wait in line for your ticket — book your spot in advance. (Especially since the lines will probably get longer as the exhibit nears its end date!). Call 0632810 to book, or — easier still for those already in Rome — stop by the Feltrinelli bookstore at Largo Argentina. There, they have a “box office” where you can buy your tickets for one of the available time slots.

And if you’re still not convinced the Palazzo Farnese is worth beelining too — let me repeat, before it closes to the public once more — check out The Economist’s enthusiastic take on the Mostra Palazzo Farnese. (After all, if The Economist says it, it must be true).