“Thieving from Athenians” quest help (minor spoilers)

I randomly stumbled on this quest in Boeotia, after dealing with the Sphinx. It requires that you find and loot a chest after finding a note about it on a soldier you kill.

The waypoint it gives me is inside of an old tall building pretty close by. The building is located on a mountain ridge south of the Military Fort of Gla, which is in Lake Kopais.

For the life of me, I absolutely cannot find a way inside of this tower. There are no windows to climb through on any side, the roof can’t be broken, and I have not found any sort of tunnel that leads up into the building from outside.

What’s weirder is that when I googled the quest by name, literally only two results came up. And on both of those sites, there is absolutely no mention of Boeotia as a region whatsoever.

I’m curious if the waypoint is glitched and I should be looking somewhere else. Anyone else done this quest?

EDIT: After using Camera Mode it’s pretty clear that nothing is in the building. So I’ll be scouting around nearby areas for a bit.