Halfpipe is a gully that leads off the top of the High Lift towards the Headwall trails.
When you follow the signs for the Headwall from the top station of the High Lift, you'll get on a traverse that opens up into a natural gully with big rocks on your right and trees on your left with moguls or powder in the middle.
If you stay right at the top of the trail you can access the Upper Triangle, Angle Gully and Rabbit Ears section of Headwall, or you can stay in the gut of the Halfpipe gully and you'll see trail signs for Headwall Glades and the Headwall.
If you traverse right you can access the Headwall and Powder 8 Gully.
You can access the Headwall Glades by continuing into the trees or staying on the traverse on your right for a little.