The Underground was a place introduced in D/P/Pt. After arriving in Eterna City, you can find an old man who will lend you an Explorer's Kit. Using the Explorer's Kit you could travel down underground and have whole new adventures. You could dig for ancient fossils which could be revived into Pokemon such as Cranidos and Sheldon if brought to the museum in Oreburgh City. A feature from the 3rd Generation was also brought into The Underground, you could create Secret Bases which you could customize with items you had received for completing tasks or that you had bought from a Hiker who would want a certain sphere.
You could also find evolutionary stones and other rare items while mining, which you could bring back to the surface with you. There were fun mini-games such as stealing flags from your friend's bases while dodging any traps they might have set along the way.
So did you like the Underground? Was there anything you were disappointed with and what did you think of the minigame and any other features? Discuss!