How to make a Secret Base in the Grand Underground of Pokemon Brilliant Diamond & Pokemon Shining Pearl for the Nintendo Switch!
Once you get to Eterna City speak with the NPC inside the Underground Man's House to get the Explorer Kit, use this to go underground then come back up and speak with him again, this time he will tell you to find treasures hidden in the walls of the Grand Underground.
Do this then once you have succesfully dug up any treasure come back to him one last time to get the Drilling Drill which will allow you to create your Secret Base anywhere you want in the Grand Underground by presing "A".
