From 93 North or South, take Exit 23 (the Government Center/Purchase Street exit), keeping left as you come out of the tunnel. Turn left on to the Surface Road (Purchase Street) and continue for about a half a mile. Turn right on to Pearl Street. Ten Post Office Square is the fourth tall building on your right. There is a parking lot on the left, underneath the Post Office Square park, and street parking on Milk, Kilby, Batterymarch, and Oliver Streets.