The restaurant awaits diners, five meters (16 feet) below the surface.
"The Pearl" is a two-meter wide white sphere tethered close to the pool's floor.
The diners jettison their weighted belts before swimming underneath and up into the pod that looks like a cross between a lunar landing craft and a giant spaceman's helmet.
Food is served by expert scuba divers who deliver foie gras, lobster salad and champagne in waterproof cases before leaving the diners peering out of the portholes.
John Beernaerts, who founded the NEMO33 pool in the Belgian capital a decade ago, has pioneered this eatery.
The restaurant, where an underwater meal costs 99 euros (USD106) per person, took more than a year to build and multiple attempts were needed to perfect the design, mechanics and food delivery system.