The Galatic Key is needed to open the doors throughout the Galatic HQ Warehouse and the Galatic HQ in Veilstone City. Without it, you can’t take down the infamous Team Galactic. This key, however, can be a bit tricky to find. Here is where you can find the Galactic Key in Pokémon Brilliant Diamond and Shining Pearl.
Before you can gain access to the Galactic HQ Warehouse, you first need to get the Storage Key by talking to the Team Galactic guard in front of the Galactic HQ in Veilstone City.
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