Add the ability to look at the stars. The concept is that every supergrid on the map will have a constellation assigned to it, and an additional major star will be assigned to the Ring of Brodgar. When the "Look at the Sky" button is clicked, the player will receive a dialog box telling him under which constellation he is, and how far he is from the Brodgar star.
There are a few details to it:
There could be a specific expensive skill for this, "astronomy".
An astrolabe or something of the sort could be necessary to perform that action.
And it would only be possible at night.
I like the idea of certain actions only being possible at night or during the day, and this feature would certainly be an immersive and elegant way to locate ourselves on the map.