It is called Massandra, in Yalta. Go to the Crimean Palaces threads it is discussed there. There are still some very very old bottles left in the cellar from the time when it was Nicholas' personal property, he inherited Massandra from his father.
Your mother must be quite special, as the 100 year old bottles still bearing the labels from the Imperial Cellar are VERY expensive, usually on the order of $2,000 USD each or more.