Federal agencies should be required to use public facilities (federal, state, or local government buildings/sites) for agency conferences.
Across the United States there are some 629 public 4-year institutions and 1,047 public community colleges. These institutions of higher education are located in every state and many times in major cities. Some even have adequate dorm or hotel accommodations as well as catering services.
Or consider military academies, other military installations, or law enforcement campuses. "The FBI is not called the “West of Point of Law Enforcement” for nothing." The FBI has more than two dozen classrooms, eight conference rooms, twin seven-story dormitories, a 1,000-seat auditorium, a dining hall, a full-sized gym, and swimming pool on a 385-acre campus.