Every December, Christine and Donald Harvey host a 200-person, black-tie Christmas party at their Fairfax home. Last year everyone spent the evening in the basement.

The Harveys—he works for Kforce, a professional-staffing firm—had recently renovated the once-dark cellar into a bright space perfect for entertaining. The first surprise is a 500-gallon fish tank behind a 26-foot granite bar. The couple thought the aquarium would add life and color to the underground space. Plus, says Christine, “I’m a scuba diver, and my husband has this love affair with water and the sea.”

The vivid synthetic coral and colorful fish—yellow tangs, clown fish, porcupine puffers, hawk fish—inspired the basement’s palette of golds, reds, oranges, and salmons.

Around the corner is a billiards room, where a coral-colored-felt pool table stands on a slate floor. In another room is the home theater that Donald, a movie buff, had always wanted.

At the party, guests were shooting pool, hanging at the bar, watching TV on the five plasmas. “In years past, everyone gravitated toward the kitchen,” says Christine. “This year, they only went upstairs to get more food, then came back downstairs.”