Stone Mine is an Outer Domain where the Stone is produced.

Gold Mine is an Outer Domain where the Gold is produced.

Iron Mine is an Outer Domain where the Iron is produced.

Buildings can't be constructed in Mines. Initially there are only the Main Building and the Abandoned Merchant Guild. In order to transport resources from Mines it's necessary to train a Merchant in the Abandoned Merchant Guild. If more Merchants are needed it's necessary to upgrade the Guild building by as many levels as you need, but not more than 7.
Mines also have a "Tunnel". It's an analogue of the City Gate, including the automatic opening after 7 days since last login. Buildings don't get damaged in Pits due to the closed Tunnel after 3 days as they are situated "inside the wall".
It takes 5 minutes to open a Tunnel and 6 hours to close it.