Russian architect and artist Andrew Beloborodov designed the apartments for Felix and Irina. He shares some interesting info in his memoires. I am reporducing the entire extract:
The main room has not been brought to an end because of the war, but soon gets a new Beloborodov, most complex, responsible and important task: "The building of apartments and furnish young Prince Yusupov, soon to be married to the niece of the Emperor Irina. <. ..> apartments for young Yusupov was designed ground floor of the left wing of the palace with its own entrance and fourteen windows on the Moika, and with adequate buildings with windows to the garden. exclusive purpose of this apartment unit depended on many factors. First of all personality and character Young Felix Yusupov was quite unusual, but it depended on all decisions. princess sometimes present in the discussion of emerging issues or in the provision of projects, but never uttered a word, she was very shy, and those who knew little of it, of the resulting a completely false impression of coldness and even arrogance. Once during a discussion of a project Yusupov came a few minutes. Left alone with the silent beauty, Andrew incredibly embarrassed - but even more confused princess, and her gentle, like a white lily, face flushed bright red. So they sat in silence until the prince returned, resuming the previous meeting. When discussing future work, he gave free rein to their imagination fly, quite regardless of any difficulty or the feasibility of their ideas. Sometimes these ideas were muddled and even absurdities, and in these cases, it was not hard to convince him to give it up, but he is often a task that it is due to their difficulty and surprise it was interesting to resolve. For Irina Alexandrovna, in her private quarters, you had to make a crystal bath and "fountain Tears "- and soon silvered walls and vaults of the Small alcove room, painted with fantastic flowers and birds, the water started to overflow drops from one pan to another bowl, these bowls were carved from colorful Ural stones - a crystal bath remained in the project, which has seriously studied . to Duke built a swimming pool, floor, walls and steps that have been made out of huge solid tiled stoves. (St Petersburg's famous sculptor Kuznetsov, who founded the factory majolica and grafted to fulfill these tile, Beloborodov told that most of them burst before they could needed to make the pool liner plate.)
With boudoir Irina Alexandrovna Yusupova at will, was designed for jewelry stash, and the aim was to Princess could see them all at once and make your choice at the evening. Here's how Andrew solved the problem: a small hidden door opened into a narrow the gallery done in wall thickness and leads to a low octagonal room whose walls consist of metal doors. It was enough to push the secret button to the upper part of the door fell open and brightly lit shop windows with all the sparkling jewels. This "magic cave Aladdin" was at the same time and carefully hidden safes.
Another more extensive stash, was held at the library, in a fall through a small door hidden behind a cupboard, which rotates together with all books. Incidentally, Yusupov wanted the air in his room came from the garden, and that his idea was implemented with an elaborate system of hoses and special filter room. There were many oddities in all apartments, but most of all to the extent that was intended for the possible arrival of the prince in the periods when the princess was missing and the state apartments were closed. There was a maze of small rooms with a spiral stair going down to the dungeon, which was to serve as a dining room.
* Apologies for the poor English grammar, I have translated it from original Russian using Google Translate