Festival of Lights
at the Mormon Temple in Maryland. Its gardens are adorned with 950,000 lights for the whole month of December and are open for free to the public. Each night, there is also a concert in the evening in the visitors' center (the Temple itself is only available to members of the Mormon Church). A few more shots in the extras (and a whole lot more on my FB page).
While we were waiting in line to see an exhibit of 95 nativity scenes from over 50 countries in the world, we struck up a conversation with two Mormon gents, who had just arrived in D.C. for their two-year mission. It is their first time out of Utah (where the Church is headquartered) and they were a bit 'wide-eyed' about Washington D.C. -- though they told us that the light exhibit back in Salt Lake City encompasses 3 millions lights. And there you have it :)