Riverside Lounge is behind New South Hall. As the name implies, it overlooks the the Potomac, so it's on the South side of campus. You can walk up Prospect St., and follow the road into campus. They'll be plenty of signs pointing towards the right direction.
If you're worried about tickets, we'll be selling them in red square on campus from 10-5. Or if you know anyone who goes to school there, ask them to buy them for you.
As for parking, your best bet is to pay for parking in the parking structure by the canal road entrence. I have friends who buy the 2 hour pass that costs $2 and just park there all day-- they never really check the exact times. You can access the canal road entrance by making a left after crossing the key bridge.