Themed vacations are a lot of fun if you have a particular interest and are traveling to a place where that interest was born, cultivated or has a lot to offer. London is a world-class city with lots to see, certainly, but it's also rich with theatrical history. A visitor could see Shakespeare's Globe Theater one day, and then travel to Shakespeare's birthplace in nearby Stratford-Upon-Avon the next day. A trip to Northern California has lots of outdoor pursuits, or it can be filled with visits to the area's great number of wineries. There are no rules, and if you only want to see and do certain things, it's a great way to overload on a favorite pursuit.