Fort Belvoir (VA) -- What's to see and do?

You're also a hop, skip, and a jump away from Civil War Battlegrounds in places like Manassass, Arlington House and Cemetery, a short drive to the beach, Maryland, etc. There's a ton to do and see sir.

We enjoyed our time while stationed there a few years back.

Not much, but you can go North to Alexandria/Arlington & DC. For great food and music in Alexandria go down King street towards Old Town. Listen and follow your nose.
In DC, my God man! Free museums during the day, Night life on the U Street Corridor, Adams Morgan area (by the National Zoo), Embassy parties, and the list goes on. All the government buildings are downtown, so you need to push out to get to music and decent food. Don't eat the street food. Google any topic of choice for DC and you'll see a decent list.
Arlington, you have the cemetaries, and food, need more DC or Alexandia for night time entertainment.
I lived in DC for 11 years before transfering to NJ. Trust me, there is PLENTY to do!
Let me know if you have more specific questions.

Is this a trick question, CPT Chris Loomis? You're just a few minutes from everything in Washington, DC, when you're at Fort Belvoir. LOTS to see and do there.