A hole

A hole is a place between the shop and another shop. You can use a shovel bought from the shop to dig, afterwards you have to fight some enemies to get down to the part you're actually looking for. Down there, there's an iron mine, a training center and a small hole.

The iron mine
This is a place where you can buy mining machines for iron bars. These machines give you an increasing number of iron bars a second the more machines you have. It is cheaper to buy a lot at once because every time you click, they get more expensive.

The training center
In the training center you can get a skill. There are two options, thunderbolt and invulnerability. Thunderbolt does a lot of damage while invulnerability makes you invulnerable to any attacks during a number of seconds. It is possible to upgrade both skills (costs gold bars)

There is also an option to test my skill, which costs 20 gold bars, this will make you fight against the training bot. Your damage will go one up every time you win against it. It is always 4 damage stronger that you and has more health (about 20), but it doesn't have a skill and potions.