Switzerland's St. Moritz ski resort serves as a winter playground for the ultra wealthy.

And within the resort sits the most expensive house for sale in the country, on the market for $185 million. As featured on a recent episode of CNBC's "Secret Lives of the Super Rich," the lavish home includes everything from a hidden library to an underground lake.

"This castle was designed to make a billionaire's jaw-drop," luxury real estate broker and listing agent Senada Adzem tells "Secret Lives of the Super Rich."

Let's a take a look inside.

Hidden behind the estate's relatively modest stone and glass facade, the winter getaway houses seven floors centered around a massive six-sided staircase, which serves as the home's backbone. The staircase itself is a feat of engineering — it shows no visible support beams.