The Hollow Tower was the first aerial arena built in Sharn, and it's brought a lot of gold into Hareth's Folly since. Most windchases occur outside of the towers, but Skyblades matches and many other aerial sports are played within the tower.
The Hollow Tower is exactly what it sounds like, a multi-story tower with all of the levels hollowed out to make one enormous domed arena, lined with everbright lanterns that keep it lit at all times. As the city has grown, many of the more prestigious events have moved to other districts, but the Hollow Tower is still frequently used, and many teams use it for training.