This is one of the most popular tunnels to explore because of it's length. Notable attractions include the popular "Lockel Library" (the sign actually reads "Locked Library" but has faded) and the purported "underground locker room." If you're going to explore steam tunnels at Virginia Tech, don't miss out on this one.
This tunnel begins right where the Cassell-Barringer run ends. I'd recommend going it at the grate in between Barringer and Miles. It's shielded from Washington Street by bushes and this quad is usually pretty quiet, it shouldn't be too much trouble to get it open, especially since it's hinged.
After you enter at the grate, crawl into the main tunnel. It's about as cramped as the Cassell-Barringer tunnel, but it opens up after a while (near Owens, I believe). You'll want to take a right so that you are heading north toward East Eggleston.
I'm not exactly sure where this happens, but soon, you will find yourself in a puddle of water on the floor. It's like this until the tunnel opens up, so you'll want to get used to it.
As you continue on straight, you will notice basement accesses to what I believe are Miles, Barringer, Newman (possibly Vawter also), and Owens. It looks like all of the accesses have locked grates, but I haven't tried any of them.
After you pass the basement accesses, there's a short ladder down. At the bottom of the ladder, all the water drains into the floor. The tunnel continues on straight until you hit the intersection of sidewalks next to East Eggleston. Here, there's a ladder up to a higher section that runs under Kent Street. There's a bunch of short turns as the tunnel goes under the street.
After you cross the street, the tunnel opens up into a pretty cool section. There's lots of graffiti here, including some left by B. in 2009. From here, the tunnel runs straight under the sidewalk next to the library and Torgersen Hall. They recently installed a new pipe in the center of the tunnel, which can get in the way at times. It's insulated pretty well though, so jumping over it isn't a problem. We had to cross it a few times while heading up the tunnel.
On your right, you should notice a subtunnel running off toward the library. It's pretty easy to miss; I missed it when I did this run, so I don't have any information on it for you. It's supposedly blocked by some pipes, but you should be able to weasel your way between them into the subtunnel.
In the main tunnel, after you pass the entrance to the subtunnel, you will notice a pretty cool subtunnel on the left side of the tunnel running off toward the War Memorial Chapel. I've heard that there is a motion detector near the door in this run, but I'm not sure whether or not it's turned on, and if it is, if anyone will even care that it goes off. Still, I would avoid it if you can.
Back in the main tunnel, the tunnel crosses Alumni Mall and passes Torgersen Hall. On your left, you will notice that one of the entrances to the grates along the left side is marked "good exit." It's not. The grate is actually located inside the bus stop in front of Torgersen.
Shortly after the "good exit," there's a 45 degree turn to the right. Above, the road to the Torgersen parking lot crosses the tunnel. Next to the Performing Arts Building, the tunnel turns 45 degrees back to the left and continues straight. Next to Femoyer, you will notice that behind some pipes, the Burruss-Femoyer tunnel runs off behind McBryde. Straight ahead, the tunnel turns to the right and the large (and hot) Femoyer-Power Plant run begins.
Unfortunately, there aren't really any good exits on this side of campus. You'll probably end up having to make your way back to Barringer. If you're exiting there, I'd recommend using the manhole rather than the grate because the manhole is harder to see if anyone is awake in their dorm and happens to be looking out of their window.