Path to Greatness

At the very beginning of the game, a message appears about a field where someone was digging something. I searched everywhere – I don't understand what the point is. I tried to dig there, but it's not possible.
Also, it's unclear what the plot twist with the lighthouse is. I captured the lighthouse, read the message that a ship will arrive today and I need to wait at the pier; then ghostly dragons appeared, I dealt with them, and waited for a couple of days; and...?