Hexgates

The Hexgates are the great Hextech tower in Piltover that teleports ships in and out of the city, the most visible product of the Hextech that Jayce Talis is responsible for creating. In season 2 an anomaly at the Hexgates throws Ekko and Heimerdinger into a parallel universe, where they build the Z-Drive to find a way back. The top of the Hexgates is also where Jayce takes the fully corrupted Mercury Hammer from his alternate self and uses it against Viktor.