The Hampton Inn and Suites in Herndon is about 1 mile (along a regional walking/biking trail) from the Reston Town Center stop on DC Metro's Silver Line, which can take you to downtown DC and its various monuments and museums.

On the Herndon side, the Smithsonian National Air and Space Museum's Udvar-Hazy Center is just down the road (a 15ish minute drive) and has a literal Space Shuttle on display.

The reception venue, Frying Pan Farm Park, is also a county park that includes a working farm (and farm animals!) and a few short hiking trails. On Friday and Saturday evenings in December they are hosting a Holiday on the Farm event with wagon rides and Christmas lights and "festive farm charm."

If you're looking for something to do earlier in the day on Saturday, the Herndon WinterMarkt will run from 12 to 7 in the heart of historic downtown Herndon. Food, drink (including glühwein!), vendors, music and dancing, etc. Apparently, the German Embassy described it as "one of the best German-style markets in the U.S."