It would be nice if there was some indication of how many you collected and how much still to go, and where to find them.
I get that a big UI wouldn't really fit the whole setting, so some sort of placing them at the monument and some interaction there to get pointed at the directions for the missing ones might work well.
While the look of the skybox fits quite well, its pixelization doesn't. A similar one at a higher resolution would be better...
Whether one could cross a fence or not was rather erratic. Maybe have at least two different fence images (one with barbs, one without?) to differentiate them, or leave it completely passable (except for where it might actually be necessary to confine the player from dropping off the map)...