Skyline is another ultraclassic easy climb at Seneca. As such, you'll want to get an early start as it is pretty much continuously occupied on summer weekends.
Hike in from the parking lot across the bridge and take a right at the sign to Roy Gap Road. Hike to the gap and a little past until you see the sign for the east face trail. Start climbing up the steps. Skyline is the first (southernmost) climb on the east face propper about 25' from the end of the rock. The route starts up a fairly obvious face/crack after a short, broken wall.
P1: climb the face between massive flakes utilizing the cracks as neccessary. Gear is good. Surmount a small wall on the left or right and belay on an airy ledge dirctly at the end of the main Seneca fin. A pair of eyebolts marks the belay.
P2: The first step of P2 is definitely the psychological crux of the route. Traverse to the left into a steep chimney. Below you is about 100 meters of air and a loooong drop directly over Candy Corner and Ye Gods and Little Fishes. The move isn't that hard, but it is wildly exposed and very committing. If it makes you feel any better, you'll be knocking pebbles down into that void for the rest of the pitch!
From here the going is easy as you ascend the chimney to a broad platform with a large boulder and tree. You probably won't be at the end of your rope yet (unless the 'airy step' really got to you!), but communication with your second will be a problem.
P3: From the ledge head up a second, shorter chimney on jumbled, easy rock to a sandy ledge (the south end of Lower Broadway Ledge) and belay. If you set directionals, you can belay from a large pine. Otherwise, you'll have to rig something more precarious in the chimney itself.
Descend by climbing up and over the ridge to the west (3rd class) to Humphrey's Head and descend the standard west face trail (the 'Stairmaster'). I believe it is also possible to rappel from the east face using double ropes, but have not done so myself.
Standard Seneca rack of medium stoppers and cams. A few large peices come in handy in the chimney (#3 camalot and up) while a #5 BD Stopper can be used to protect the airy step. Bring long slings for anchors at the belays. A 50 meter rope is sufficient for all pitches.