When Robert Montagne and his colleagues at Walnut Street Development in Fairfax, Va., first contemplated building Clarendon 1021, a 420-unit condominium building in Arlington, Va., deciding whether a fitness center would be included wasn't up for discussion. "With a building of that size, a fitness center was an absolute necessity," says Montagne, company president. "It was a no-brainer. With all the competition at that level you need those kinds of amenities."