Getting the gold key hanging on the wall of the desk in the lobby of the hotel will be one of your first challenges in Luigi’s Mansion 3. You’ll need to know what abilities that you have at your fingertips as you’ll need to use one of them to access the area behind the hotel desk.
Use the Burst Move to get the key
What you’ll want to do to get access to the gold key is to press the ZL and ZR buttons to jump into the air using the Burst move. This will open the pathway blocked by the gate and allow you to get close enough to the key to interact with it and take it.
Once you have the key you can simply head to the door at the top of the stairs to progress in the game.
Bonus items, once you’re behind the desk you can hit the green light on right side of this area with the Strobulb. Simply charge the strobe by holding A and then releasing. This will reveal a hidden area and a purple gem.