Get the dowsing machine app on your poketech and look for it using that. It is in between the hotel and her house.
Submitted by awesomeness
ok the key should be just outside of hotel grand lake (the hotel the girls at) in the back where the lady who heals your Pokemon not in the hotel itself but outside in the back you will need the scanner to find the key but its on the pavment :D
Hidden. Use the Dowsing Machine in front of the exit of the hotel
First, go to Hotel Grand Lake which is near Lake Valor. Talk to the lady standing near the door. She lost her hotel key so with your poketch, go to drowsing machine. Once you find the key, talk to the lady again. She will reward you with the white flute.
Go into the hotel entrance (the one that says "Hotel Grand Lake Another World on Lake Water" on the sign in front of it) on route 213. Exit out the notrth door. Take a pace left, then two (if not, try a third step) steps north. Press the A button and you will have found the key.
Mumbai
right next to the back of the hotel in valor lake place
One can find information about the reservations at the Lake Hotel in Killarney on websites like hotelcombined and yeego. One could also go to the reception at the hotel itself and ask for information.
use your dowsing machine and use it right next to the healing guys house, then a mark will appear, talk to the hotel girl and she gives you a reward.
you have to be a member like me
Lake Hotel was created in 1903.
if you are inside the hotel, go to the top door(↑), and use itemfinder. it is near there.
Go to Valor Lakefront.Enter Hotel Grand Lake then exit to the back door.Go one step forward and look left.And there it is,the suite key