Battalion,
Here you go.
In DC the Club Acela Lounge is located behind the information kiosk, which is in the center of the waiting areas between gates D & E. There are two large wooden doors there, ring the bell to the right of the door and the attendant will let you in. Show your tickets and you’re in. They will escort you to your train when it’s time.
As for railfanning while in the station, the best place is the parking garage. Also located near the center of the main passenger waiting area is an up escalator. Ride that up one level, turn right and head out the doors. In addition to the parking garage signs, you will also see see for Grey Line tour buses. The actual garage has three levels if memory serves. Most provide a nice overall view of the station, plus you can see up the corridor to the Ivy City Yards.