Not really a delicacy, but kind of a local flavor that you can't find anywhere.
Roy's place in Gaithersburg. Over 200 different kinds of sandwiches. Sadly, Roy passed away a few months ago, but the place still carries on the tradition.
Check out the menu...
Roy's Menu -- Featuring Over 200 Unique Sandwiches
One of the sandwiches is
A Good Cold Sandwich
"Two stale heels of bread enclosing a freshly-made ice cube"