Far as I know, all chests are found inside the maze, not in the outer starting area, and there's only ever one per instance.
The ones I've seen:
- 625, 550 (enter maze, turn right, go to the end of the row, turn left, beside the fairies)
- 555, 600 (enter maze, turn left, turn right, turn right again, corner behind Blightbeard's spawn point)
- 500, 600 (left, right, right then left, left past Infiltrator Johlen, left and down at end of row)
- 565, 560 (on your left just before Prince Hylas)
- 590, 290 (at far wall behind Greenscale, next to death pool)