This one is a little different, and was not so much a birthday idea as a university reunion I had at my house.    About 20 people from way out of town were coming over, and I organized a walking tour of Oxford (luckily I live near a historic and beautiful city) with a treasure hunt thrown in. I started the planning for this about six weeks before because I only had weekends free, but could have done it faster.  Guests were divided into groups of four, and each given a map and folder. On the map was their individual route, with areas of interest and certain pubs marked.  In the folder was a large amount of information regarding Oxford and its history. We all started from the same place, and, at 15 minute intervals, left on the tour.  Although the routes were different, they encompassed the same places, and so I asked the same questions of each group - where was so-and-so buried, how many lions on the town hall etc. Part of the fun was that each group had to have the landlord of each of the pubs on the map sign their card to prove they'd all had a drink there. A few close friends from home and I waited for the groups to pass through our pub before heading on to the next one.  The day rained unfortunately, but I think that just made the whole thing more fun!    Bear in mind that when you walk the tour yourself, you'll go a lot faster than the visitors - we did it in under two hours, but it took our guests around four or five to finish. We also made each group pick up a number of bizarre things around town - a postcard of Oxford with a stamp, which was to be sent to the old master of our College, a photograph of themselves with some tourists (sorry - couldn't resist) etc etc.  The winning group was given a bottle of Champagne. I arranged taxis home, and after a hot shower, we were ready for the real party that evening!