Go to the entrance floor of the hotel. Go right 2 screens. You are now in a stone built section. Use the Kylesmore Essence that you got as a reward which you got for defeating Sir Stephens, one of the bosses in Marvel's Mansion. That will summon up the boss. Defeating that boss gets you the Key which opens the little monument which gives you something very nice, but I don't remember exactly what, at the moment.
Thank you. Not so obvious to find Kylesmore Essence is used to attract the original hotel's owner, Kylesmore's Hotel, I got it now!
If you love searching the truth, fight for human race,good and bad sex, sadism to stop, the prequel is WTF Read "The sword of Truth" by Terry Goodkind in your language or English. Read the prequel after "the Confessor" to not be spoiled.