After a while, balls just get boring. And who even goes to actual ballrooms anymore? Not Philadelphia's chapter of the American Institute of Architects (AIA). They chose a bare bones building in the still-developing Navy Yard to throw this year's annual black tie Beaux Arts Ball (Oct. 22, 9 p.m.). The glass-enclosed One Crescent Drive is still all concrete floors and naked drywall, but designers are going to transform the building into a sexy, celestial-themed ballroom in just three days. Though an unconventional choice for a soiree, unfinished buildings are what AIA is all about.

Philadelphia's AIA keeps the centuries-old tradition of the Beaux Arts alive with its 25th annual costume ball. Originally started in Paris at the L'Ecole des Beaux Arts in 1648, the party was a masquerade celebrating the end of term for young architects and artists; mingling between the typically divided social classes was encouraged. This year's event, titled Lunacy (a play on words stemming from the lunar aspects in the decoration), will foster mingling between the design community and the general public and feature a night-sky color scheme of "platinum and onyx."

The space will be divided with black and silver draperies, its atmosphere regulated by computer-controlled "intelligent lighting" courtesy of Pro Vision Productions. Unpainted drywall will be adorned with fluorescent painted celestial shapes that will appear under blacklight. Furniture, donated by Manayunk-based retailer Dwelling, will help shape the space's flow. Black plush sofas and low, brushed-steel tables will be placed in the cordoned-off VIP space to create a more intimate setting for sitting and talking, wheeling and dealing, and maybe some inconspicuous groping. High cocktail tables will be scattered throughout the dancing area to encourage movement.

Layout and lighting will be crucial to the mood. On the south side of the crescent-shaped building, the lighting will be brighter, to reflect the dance floor scene onto the floor-to-ceiling windows (and to not distract from the more breathtaking views on the north, east and west sides). On the north and west sides, the lighting will be lower to provide views of the skyline and ships in the yard. All of this will be accomplished by Oct. 22 for just $15,000.

The main events will take place on the fourth floor. Scheduled features include matchmaking, hired dancers to encourage wallflowers to get up and move, an oxygen bar for the short of breath and face painting, possibly leading to nude full-body painting — which is still being worked out.

Proceeds will go to the Center for Architecture, a nonprofit branch of Philadelphia's AIA. Tickets range from $75 to $350 (if you want to go all VIP). The money will benefit the Charter High School for Architecture and Design (CHAD), the Community Design Collaborative, as well as the Architecture in Education (AIE) program. Visit www.beauxartsballphilly.com for more.