The core area of a Union charge is still preserved at Ox Hill Battlefield Park. The rest of the battlefield has been lost to development unfortunately and the park only exists as a result of a deal between developers with local government. But I still recommend checking it out at least once. There are no shortage of places to visit in our area that are related to the Civil War. Start with the sites the National Park Service administers like Manassas, Fort Stevens, Fords Theater, Clara Barton's house, Harper's Ferry, etc then work your way out to county/state parks like Bristoe Station, Ball's Bluff, Cedar Mountain and look into non-profits or museums. The Civil War Interpretive Center in Fairfax is a hidden gem; be sure to go on a Saturday for a 1 pm tour so you can see all the graffiti drawn by Union soldiers. This weekend in Leesburg there is going to be tours + a reenactment at the 1861 Ball's Bluff battlefield park. I think the Civil War Medicine Museum in Frederick is one of the best museums on any topic in the area and you can tag on a visit to the Monocacy or Antietam battlefields with it too. The re-opening of the renovated African American Civil War Museum on U St is supposed to happen this winter too so keep an eye out for that.