I also relearned a lesson I should have remembered: avoid driving in Pennsylvania. However, I wanted to see Wheeling, WV on the way back, so I planned a route that took me through a bit of Southwestern PA along Interstate 70, then South on US 219 back to Maryland. It looked easy enough on the map.
Then I encountered this interchange near Greensburg.
Your mission is to enter the map on 70 at the lower left and exit on 70 at the lower right. That's all you have to do. I still can't figure it out. At the time, I wound up taking US 119 South and justified it as "the scenic route".
(image from Google Maps, click for bigger)