An organization called the Society for Creative Anachronism has its members roleplay as characters from the Middle Ages. They wear costumes and attend parties (called revels) in which it tries to recreate the culture of a medieval court. Why not hold a medieval-themed costume party yourself and take your guests back, at least for an evening, to the year 1200 or so?
Start With A Royal Feast
Have everyone show up in appropriate costume, the better to create the illusion of going back in time. You as the host should play the role of King or Queen and maintain some measure of control over the festivities.
You should start with dinner. The medieval cookery site offers a number of period recipes that can slake the palate of any
Then Let The Midieval Revelry Begin
After dinner, perhaps some of your guests with some talent will provide a song or a story (playing the role of a minstrel) or of a stand-up routine of jokes (playing the role of a court jester.) You could hold a “royal hunt” which would more resemble a scavenger hunt than chasing after a boar or deer as real medieval people would engage in.
Dancing was always a favorite activity in a medieval revel. If you have a room with enough space, or can be converted into a place with space, consider these dances, with instructions and steps, from Middle Ages Net. Hole in the Wall is a particular favorite, even though it technically dates from the 17th century. Other, more authentic dances dating from the period include the galliard and the pavane. Circle dances, called bransles (“brawls”), are also fun.
A role-playing game in the form of a quest would also be a great after-dinner pastime. The idea is for your guests to play the roles of medieval characters who are in search of some object, say the Holy Grail or a piece of the True Cross.
The idea, of course, is to have fun in a way most people in our hectic 21st century existence are unable to. A medieval-themed party is something your guests will remember for a long time to come.