It's the Aid Tower Colony quest. The Castle told me to go to the Tower Colony to help after the Great Portal fell, Kelner was the one to direct me further, telling me to go upstairs to get some items to help, but the doors upstairs are locked.
I searched and looked through the walkthroughs (to no avail) before asking here. And yes, Captain Bahgatis was the first person I spoke to (exhausted all speech options) before finding that Kelner was the go-to-person for the Aid Tower Colony Quest.