GDG- Fort Monroe and Williamsburg

[The Mills]

I am planning a trip to Williamsburg this weekend and was thinking of taking a side trip to Fort Monroe to see where Jefferson Davis was kept for his two years, but can't really find if this installation is open to visitors, since it is still an active base.  

Can anyone tell me if you are able to visit this?

Also:  are there any sites associated with the battle of Williasmburg still left that would be worth visiting?

Thanks
Andy