When you reach the Valor Lakefront, you will come across a hotel. If you talk to the NPC that is standing in front of the first building you see (the northmost building), she will complain about how she lost the key to her suite. Now she can’t get into her room. Since she won’t look for it, it’s up to you. Here is where you can find the Suite Key in Pokémon Brilliant Diamond and Shining Pearl.
The NPC will give you one hint as to the whereabouts of the Suite Key. She is sure that she had it when she left the reception counter. While it might be tempting to check all throughout the reception building, the key is actually out in front of it. Run south to the reception building but don’t go inside. When you reach the building, look to the left at the small hill. Press the A button in various spots on the slope until you pick up the key. The spot is very specific so you might not get it right away.
Once you have the key, bring it back to the NPC. She will thank you before heading into her room. Follow her inside and talk to her again to get a Lava Cookie. This cookie can be used on a Pokémon to heal of the status conditions affecting them.
