This item is exclusive to Terraria: Otherworld.
Purifying Tower

The Purifying Tower is an item in Terraria: Otherworld. It is a sacred structure need to purify the world. This item can be found or crafted. On activation, the item will push back unnatural forces such as The Corruption. The tower is also capable of powering other structures that require power, including the Wartower. 

When used against the Corruption, the Corruption will attempt to fight back by sending monsters out to retake the land. They will continue to attack the towers until the land is captured.