I loved being a research assistant intern at the Wilson Center. But this is an internship where you have to be proactive to make the most of your experience. The center is crawling with amazing scholars, but you have to take the initiative to reach out to them. Although I was originally paired with 2 scholars, I would offer to do research with other scholars whose work interested me. I ended up coauthoring a paper with someone I didn't even directly work with. I just talked to him about my interests and he offered to work with me. So take advantage of the wealth of resources around you!
You're basically on your own schedule and have no supervisor. Some people don't work well in this setting, but I enjoyed it. Your experience also depends on the scholar you work with. Some scholars (especially the journalists) don't really know how to work with a research assistant so you have to be clear in your communication about what you want to learn, do, and accomplish. I know some interns were paired with scholars who didn't ask them to do anything, which is a total waste of an opportunity. If this is the case, I would recommend offering to work with another person so you can build your skills and gain experience.