Unsouled

You have to had absorbed the twisted lady's soul in Act 3 in order to get this. In Act 5 after the the prison area you will reach a area with giant ice blocks all over head up and trough the middle kill all the enemies then use the soul absorb ability on the top right book shelf a door to the top left will open. Go trough the door & press Y button on the bed & the achivement will pop.