Heavensward Ending (Spoiler)

[saber_alter]

That "stargate" is actually a pretty common piece of Garlean architecture / machinery. There's one at Cape Westwind, for example, presumably to get into Castrum Marinum. I assume it's a more limited, short-range teleporter.

it is. garleans had a few smaller-scale ones at the praetorium. the ones at sea-based castrums like the one in Azys Lia and cape westwind are actually the larger scale ones, generally used for transportation of multiple soldiers and supplies in short order.