Have a champagne cocktail and dinner at Crazy Bear.
Take a day trip out to Hampton Court Palace and have your camera out at "The King's Stairs," a 1700's Italian Baroque masterpiece painted by Antonio Verrio.
I took this trip at 18 with Contiki. It was my first overseas experience and they were amazing from start to finish. If you are 18-35 and looking for a seamless vacation option with the added bonus of traveling with people from all over the world (in your age bracket) look into Contiki.