The entrance to Temple Dungeons is located in the eastern part of your farm:
Explore the depths of Temple Dungeons: use instruments acquired in Cableway, clear debris, open doors, and descend to deeper floors.
You cannot return to the previous floor once you enter a new one.
In Dungeons, you will find special chests containing uncut jewels. You can refine them in Jewelry Workshop to get bags of different jewels used to upgrade farm buildings.