I'm in Washington, DC where I am attending the American Library Association (ALA) as a member of the Association's Genealogy Committee. I will chair that committee for the coming year. Unfortunately my participation in the conference is cutting into my research time because Washington is one of my favorite research sites. The top three sites for genealogists here are:
1. The Library of Congress (LC)
2. The National Archives (NARA)
3. The Library of the Daughters of the American Revolution (DAR)
I'm on my way to another ALA meeting so I'll just introduce LC briefly in this post. Two of these organizations are libraries and therefore collect a wide array of materials of interest to genealogist. LC may be the largest library in the world and contains all kinds of materials on any topic you can imagine and in any format you can think of. The purpose of LC is to provide members of Congress and their staff with all the information they might need to know on any topic. Sometimes a way to get information from LC is to send a research question to your member of Congress and hope that the member's staff will forward your inquiry to a subject specialist in the Congressional Reference Service of LC.
I would recommend that you check LC's website even if you think you are somewhat familiar with LC. Something new is always being added. Lots of digital content of interest to genealogists is available online through the American Memory project. More is being added daily.
Of course LC is is a library and you will want to do search the LC Catalogs. This process may not be as user friendly as you would like but your results should be worth your effort. The on screen directions should help you navigate.
Visiting LC in person can be very rewarding but it is intimidating to a first time researcher. LC is an entire complex of three buildings--each of which is a square block in size. The buildings are connected by underground tunnels. Security is high as it is in most buildings in Washington. You may have to go through a metal detector and have your bags searched to enter but you won't have to take to take off your shoes as you do at the airport. You will have to register and get a picture ID that will serve as your library card. You also will have to register your laptop and camera and "un-register" them as you leave. This is partly for the security of your toys to make sure the person who tries to remove them from the building is the one who brought them in. There are always interesting displays for tour groups. You will probably want to go to the Local History and Genealogy Reading Room which has a very helpful website. LC is a closed stack library which means you have to fill out call slips and request the materials you want. It can take up to an hour for the materials to be retrieved for you. The reading room has a small but interesting collection of back runs of genealogy journals you can peruse as you wait for your materials to arrive. You can even go to one of the staff cafeterias to refuel your body without leaving the premises. I would be happy to try to answer any questions if you post them as a comment through the link immediately below.