A Skyview Tower is a tall structure from Tears of the Kingdom. They can be used to launch Link up into the Sky, where is he able to reach many of the Sky Islands. They will also update Link's map of that area of Hyrule as well as the sky.
Tears of the Kingdom
The first Skyview Tower Link encounters is at Lookout Landing. After encountering Princess Zelda at Hyrule Castle and returning to report this to Purah during the Crisis at Hyrule Castle quest, she offers to activate the Skyview Towers. With the help of Josha, Purah activates the towers, allowing Link to be launched into the air and update his map data using the Purah Pad. She also provides Link with the Paraglider.