first, you have to make your way to Enterna city [where you get your 2nd badge] and find a house that has a sign right next to it read it, then talk to every body in that house somebody will give you a explorer kit. Go to your key items pocket and scroll to explorer kit press A and save the game from how it says and guess what? your UNDERGROUND!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!1
you have to fix the power plant, go to the radio tower in lavedar, get the second radio card, and then put the radio on pokeflute station wile standing by the snorelax. exit the pokegear and it will attack.
when you face team rocket in goldenrod city the radio tower is taken over and they replace the director beat the imposter and you will get the basement key
they give it to you
in a chest deep in the forbidden forest
you find the basement key in the underground path
go to key items find it and hit use save and your in underground
in the basement of the galactic warehouse in veilstone city
The card key in Pokemon Heartgold and Soulsilver is located in the Goldenrod Underground.
The basement key is used in the Goldenrod underground. You get it while rescuing the Radio Tower from Team Rocket - specifically, after defeating a Rocket Executive disguised as the director.
You can dig up fossils underground by using the Explorer Kit in the Key items pocket of your bag :)
Underground, where you can go to by pressing explorer kit in key items in the bag. But you won't get them on your first try.
There's no item known as the Darkness Key in Pokemon. At all.
go to denver
When your in Goldenrod you goto the teamrocket infested radio tower (get 7 badges or the fighter badge first)then get to the fifth floor then an executive will fight you then tell you hes in the warehouse in the underground place and then he will give you the key but i recommend getting a guide before you do that CRAZY FRUSTRATING button maze
you need the silver wing key item