Cave will be unlocked when you find the last part of the Mysterious diagram and build the City Gate.
Tap the item to get info about it.
To build the Cave you need resources. Building takes time.
Complete tasks to get shovels you need to upgrade the cave.
It takes time to excavate from one set of ruins to another. You can speed up excavation.
There are 7 available levels of the Cave and 125 match-3 levels to beat. To upgrade the Cave you need to fulfill the requirements.
You need resources to upgrade the Cave.
It takes time to upgrade the Cave. You can speed up upgrading.