The Spreewald or Spree Forest is a UNESCO biosphere reserve whose name is drawn from the river Spree that runs through it in a labyrinth of more than 200 small canals. Besides being noted for its biodiversity, it's also home to a Slavic minority called the Sorbs. Some of their age old customs, such as delicately decorated Easter eggs, are still in brilliant evidence. Tamsin Walker went to explore.