Endumion's Nemein (Location)
A treasure location in Marmarica
A roadside camp swarming with an unreasonable number of guards.
It might be technically possible to sneak in unobserved, but it's statistically unlikely. Draw away anyone you don't want to kill outright with a good housefire or two.
Sneak into the central tent when ready and loot the red chest for location completion.