Ho, i did find the exavation dude already, i just didn't feel like doing it. I have no idea what i'm supposed to do and it just feels like one big distraction from the main campaign.
There are 4 of them, actually.
To be quite honest, I haven't gotten to the bottom of excavations yet. On the surface (ok, enough puns, sorry) you need to place explosives to unearth chests and enemies.
The chest markers indicate by their colours how good their loot is, while the skull markers indicate enemies, with the big ones being rare monsters. The markers with text on them give monsters some specific boost, but also increase loot from either chests or monsters in some way.
Among the loot, you will find currency items for the specific dude you've found in the stage. One of them will sell you items that aren't identified, working as a bet kind of deal. Another sels identified items, another sells other currency items you can bargain over and the last one sells currency for the other three (which makes his currency worth more than the other's). In particular, the most valuable currency of each of these npcs is an item that re-rolls and re-stock their inventory; and also apparently it is the only one that can be traded with other players.
Finally, there are also supposed to be maps you can find for them, but I've never found one, so I don't know much about that.