Russia, St Petersburg
A two day, guided tour, of St Petersburg in Russia - with the really excellent SPB Tours - who we really couldn’t fault*. An excellent guide, who was able to circumvent all the queues (and there are quite a number for the major attractions) for the 6 of us and an equally excellent driver. made for an unforgettable trip.
This Lonely Planet article really covers all the main sights - there really was so much to see in the two days - a some distance to travel between different areas - especially so out to the Peterhof Palace.
2023 Update - Given current situation, I don’t think that they exist any more.