Eberron: Shadow of the Mark
In Upper Central Plateau, near Highest Towers and Mithral Tower, is Skysedge Park. It is an opulent park district that includes a Gatekeeper Druid enclave among other things.
The Gatehouse is a small stone building at the edge of Carosten Park. One could easily pass by. But it is actually a sacred site to the Gatekeeper Druids, and their work in Sharn maintaining planar boundaries is organized here.