Two blocks up 6th Street from the Old State Capitol is the excellent Abraham Lincoln Presidential Library and Museum. Marie loves it and so will you if you're ever in Springfield. Donna and I were especially impressed with the wild Whispering Gallery. My words can't do it justice so you're going to have to experience it yourself.
That's John Wilkes Booth on the left in the second photo. Generals Grant and McClellan are next to the door of the White House. Partially obscured on the right are Sojourner Truth and Frederick Douglass.
Subway seems like an odd choice for a restaurant inside the museum but old Abe loved their Spicy Italian $5 footlongs. We skipped Subway and had a very tasty lunch at Cafe Brio.
I spent the night in Springfield back in 1997 on a trip from Saginaw to Albuquerque. I may have eaten dinner at Cafe Brio on that trip. The details are fuzzy but I remember eating at a casual cafe with mismatched vintage silverware not too far from the Old State Capitol. The silverware was matching this time, however, so maybe not.