You’ll start exploring Team Galactic’s Veilstone Headquarters shortly after defeating Leader Candice at the Snowpoint City Gym. However, you’ll find much of the building blocked off by hi-tech security doors.
The Galactic Key is deep inside the Galactic HQ, and it will unlock the unaccessible areas of the Veilstone Headquarters. It opens up the most important passageways and ultimately allows you to battle Cyrus for the Lake Guardians’ freedom.
Acquiring the Galactic Key Inside Galactic HQ
After winning the Icicle Badge from Candice at the Snowpoint City Gym, your next objective is to investigate Team Galactic’s Headquarters in Veilstone City.
But you won’t be able to enter the Galactic HQ through the front—you’ll need to get Officer Looker to let you in through the Galactic Warehouse using the Storage Key.
After Looker opens the Warehouse door for you, follow him inside.
Now that you’re within the walls of Team Galactic’s base, head east down the hallway.
At the first corner, you will come across one of several Galactic Grunts to battle. Defeat this Grunt and continue heading northeast.
Note: None of these Grunt battles is particularly hard; the Grunts generally use the same Golbat, Houndour, Stunky, etc. that you’ve come to expect. But keep in mind that they’re all around level 40 and can wear out your team if you’re not careful.
A second Grunt is guarding the next corner. Defeat him and continue up the stairs.
The Grunt in the next room has no Pokémon and can’t battle you, so pass him and head up the opposite staircase.
In the northwest corner of the next room are a pair of yellow circles on the floor. These are warp tiles; stepping on one will teleport you to another warp tile elsewhere in the building.
Fight the Galactic Grunt guarding the hallway, then step on the left-hand warp tile.
Step on the warp tile in the next room to continue.
Then head up the stairs in the next room.
You will emerge on the next floor in the middle of a hallway. Head to the left end and step on the warp tile.
Now cross the next hallway and go down the staircase to your right.
Downstairs, circle around and head west.
There is a Scientist trainer here for an optional battle. Head around him and take the staircase at the northwest corner of the room.
Go west down the dim dank hallway.
Defeat the Galactic Grunt you’ll find here, then circle around the boxes to the west to find a Poké Ball item on the ground.
Examine this Poké Ball to obtain the Galactic Key.
Galactic Key Details and Uses
You can use the Galactic Key to open up all the locked doors inside Team Galactic’s Headquarters.
To use it, simply walk up to a security door and press A.
Then select Yes to open the door permanently.
The Galactic Key will open shortcuts (including through the front entrance of the Galactic HQ) and lead you to new items.
But the Galactic Key’s most vital purpose is unlocking the door to Cyrus’s office so you can defeat him in battle a second time.
Victory in this battle will result in Team Galactic leaving Veilstone City for good.
It will also allow you to free the three Lake Guardian Pokémon, whose power Team Galactic has been attempting to harness.