UnderGround Base

To create an Underground Base, you must buy a Diggers Drill from an undergrounds sales person, and use it against any wall you want.

Hope this helps you!!!

Or you get it from the digg guy in the 2nd gym city by completing his tasks

To make a secret base you have to get a digger drill. You can obtain one from the underground man in Eterna city once you complete a certain number of missions that he gives you or you can also get one from a hiker in the underground (I think there is only one hiker that sells them so search thoroughly). You can also change your secret base by using a digger drill PS: I hope this answer is useful

To make a base in the Sinnoh Underground, you must find an item down there called a Digger Drill. Buy it and you'll be able to make a base. When in, you will see a bunch of rocks. There is only one way to remove those. To get all of them, you must capture 50 flags from a friend in the Underground. Once completed, you'll be able to remove every single rock in a base.

Hope this helps,
Sk8rboy

First, you need to find a good sized sphere. To do that, touch the touch screen and look for shining spots. Then walk to a shining spot and push a to dig into a wall. Then, try to uncover a sphere. Next, go to a guy underground that sells traps and buy a digger drill from him. Then, go to a wall and use the drill. That will be your Secret Base.

The only things that are dangerous are the galatic bandits that steal all your Pokemon if you walk into a certain place hope this helps.