Hi,

In temple on the lake, you need to block off the water before you can access the boss. Near the back of the dungeon, after the in-game-event, push the huge stone into the aqueduct on your right. Then return to the main gate and you will be able to pass the gate, save, and fight the boss.

As for the forest and mine. Those are optional dungeons and you should wait until you are a higher level before completing them.

Good luck!

The game-play event where Alicia talks to Leone once they reach the aqueducts. (This is where you find the stone that you push to the right, blocking off the water)

Right after that event, you will find a big stone a little bit to your left. (Run to the left) You can't miss it.