The Frozen Princess is a Time Limit challenge on Floor 5 introduced in Series 4.
The Caretaker's explanation to the Game:
"There once was a princess, cold hearted and mean. Frozen inside and out, wake her up and she'll scream. To warm her sub-zero heart, unfortunates must gently place five flowers one by one into her chilly blue hands. Sounds easy eh? But someone's out to upset her."