This year the Grand Ducal Palace attracted more than 10,000 visitors. The GDP is traditionally open from July to August each year. This coincides roughly with the time when The Grand Duke is on his annual holiday in Bromes-les-Mimosas in the South of France.
The proceeds of the guided tours are given to the foundation established by The Grand Duke and Grand Duchess early in their marriage. This year 28, 027 Euro has been paid to the foundation as a result of the tours.
I tried to find the website of the foundation with no luck. There used to be a website which seemed to always be under construction.
Article in ghetto English.