Well, you might write about medieval pilgrimages, which were an interesting custom. People used to go on pilgrimages to visit religious shrines. The most important one in England was St Thomas a Beckett's shrine in Canterbury, and Our Lady of Walsingham in Norfolk was another important one.
People of all classes used to go on pilgrimages (as you can see from Chaucer's Canterbury Tales) and it was more than a religious experience, for many people it was an adventure and a holiday as well.
Another interesting topic to write about might be medieval castles, what they were for, how they were built, the kind of people who lived in them (a castle was a whole little world of all sorts of different people and activities).
Some interesting events from the middle ages you might write about include the Viking raids, the Norman Conquest, the Crusades, the war between King Stephen and his cousin the Empress Matilda in the 12th century, King John and the Magna Carta, the murder of Thomas a Beckett, the Black Death, the Hundred Years War, the Wars of the Roses, the invention of printing, Richard III and the Princes in the Tower, the travels of Marco Polo, the painful story of Abelard and Heloise.