In this Lego set you can build Elsa’s Sparkling Ice Castle, which includes a secret staircase.
It has 292 pieces and includes Anna, Elsa, and Olaf. It also comes with skis, skates, and a tiara (plus a carrot nose for Olaf, which I thought was a nice touch).
The age suggestion is 6-12, although I certainly could see a four or five year old enjoying this if they had a parent help them build it and if their frustration level is not too high.
My son is particularly crazy about Lego sets (although not princess castle ones), and one of the things that’s great about Legos is that building it is just the beginning. After you finish building it, you can spend hours playing with the set you created.