I was a MIDN 2/c at Penn State. It was a Tuesday; I remember we did PT outdoors in the parking lot of Shields Building, the registrar/bursar/admissions building by Beaver Stadium and East Halls. My first class was an IST class where we were doing group projects. My group was ahead of the curve, so we had a quick powwow, cleaned up some stray cats and dogs and went home after 20 minutes or so.
I took a nap, and was asleep went it started. Woke up none the wiser and went off to my 1015 class: The History of Islam. The prof said "a plane" hit the WTC. Like many here, I thought of the B-25 hitting the Empire State Building in WWII, and figured it would be a minor thing. Just in case, the prof cancelled the syllabus for the day, and we spent the day talking about the Islamic connection to terrorism and religious extremism, and the Islamic law of war.
My roommate was parked in front of my computer when I got back; I had a TV card which was our only connection to cable. That's when I found out that the towers had gone down. Later, I ran by the hole in the Pentagon during the '01 Marine Corps Marathon. Plenty of armed Marines with loaded M-16s around the course where it wrapped around the building.