Dwyane Wade & Gabrielle Union -- We're Getting Married ... IN A CASTLE!!!!

Here ye, here ye ... Dwyane Wade and Gabrielle Union are swapping "I dos" today in a famous MOATED CASTLE hidden away in Miami, FL ... TMZ Sports has learned.

The place is called "Chateau Artisan" -- considered one of the coolest pieces of property in the country ... and it's also where Birdman shot his 2010 music video for "Fire Flame."

Dwyane and Gabby have been going to extreme lengths to make sure their wedding is super private ... which is why this ultra-guarded estate PROTECTED BY A MOAT appealed to the couple.

We broke the story ... the couple is making their guests sign confidentiality agreements -- and have also banned social media from the event.

As for the property -- we're talkin' 19,000 square feet, 8 bedrooms, 7.5 baths ... and sits on 14 acres.

Sources tell us workers have been on the property for the past couple of weeks making sure the place looks PERFECT for the couple's big day.