The best place to find lecture halls in Washington, D.C. include educational institutions like universities, high schools, and academies. The Martin Luther King, Jr. Memorial Library is one such institution, with a Great Hall, auditorium, and 5th floor event space suitable for lectures. Washington, D.C. also has one of the largest concentrations of museums of any US city, most of which have classrooms and
exhibit halls for presentations and other special events.
Lectures can also be held in art galleries, churches, and community centers since these buildings will usually have a classroom or two for training or special events. Business centers, offices, and coworking spaces offer rooms suitable for lectures as well. Hotels that cater to business clients will have lounges, banquet halls,
meeting rooms, and other venues that will comfortably seat hundreds or even thousands of attendees. What's more, a hotel experienced in hosting lectures will have projector screens, microphones, stages, and other amenities for rental.
Hotels are also great lecture venues if you're expecting a lot of attendees to be coming from out of town. You'll be able to hold the lecture in the same building where guests will be sleeping and eating, for convenience.